(Pronounced "myew-lah") UNIX standard audio file format.
Refers to making web pages available and readable to all users,
including those with disabilities such as sight or hearing
Audio Interchange File Format. Standard audio format originally
developed for the Macintosh, which is now supported on PCs as well.
It is one of the formats commonly used for distributing audio on the
- alpha channel
In graphics, an extra channel for storing information about an image.
The alpha channel works like a mask that applies properties (such as
transparency) to the pixels in the image. Other channels typically
include color value information -- as in the red, green, and blue
channels of an RGB image.
- alpha-channel transparency
The method of transparency used by 24-bit PNGs, which use an
additional (alpha) channel to store variable levels of transparency
(up to 256) for each pixel in the image.
- animated gif
A GIF89a that contains multiple frames and a "control
block" for controlling the animation timing and display.
A self-contained mini-executable program, such as one written in the
Java programming language.
- ASCII files
Files that are comprised of alphanumeric characters. Some FTP
programs refer to ASCII files as "text" files.
Active Server Pages. The part of Microsoft's Internet
Information Server software that allows server-side scripting for the
creation of dynamically generated web pages and database functions.
Web pages created with ASP commonly have the suffix
- audio bit depth
The number of bits used to define the resolution of the amplitude (or
volume) of a digital audio waveform -- the more bits, the more
accurate the rendering of the original audio source and the larger
the resulting audio file. Some common bit depths are 8-bit (which
sounds thin or tinny, like a telephone signal) and 16-bit, which is
required to describe music of CD quality.
Audio/Video Interleaved. A digital video format developed by
Microsoft in which audio and video information are interleaved in
every frame for smoother playback.
- binary files
Files made up of compiled data (ones and zeros), such as executable
programs, graphic images, movies, etc. Some programs refer to the
binary mode as "raw data" or "image data."
Common Gateway Interface. The mechanism for communication between the
web server and other programs (CGI scripts) running on the server.
- character entities
Strings of characters used to specify characters not found in the
normal alphanumeric character set in HTML documents.
- character set
An organization of characters -- units of a written language
system -- in which each character is assigned a specific number.
A software application that extracts services from a server somewhere
on the network. A web browser is a client that renders and displays
documents on remote servers.
Color Look Up Table. A list of colors and associated index numbers
used to render eight-bit images.
Cyan-Magenta-Yellow-Black. The four ink colors used in process
printing. Not appropriate for generating web graphics. (RGB is the
color mode for web graphics.)
Compression/decompression algorithms applied to media files.
Cascading Style Sheets. An addition to HMTL for controlling
presentation of a document, including color, typography, alignment of
text and images, etc.
CSS with positioning. Refers to a proposal for adding positioning
capabilities with style sheets. The CSS-P proposal has since been
rolled into the CSS2 Specification.
- data fork
The portion of a Macintosh file that contains the actual data of the
document. See also resource fork.
- data rate
In video, the rate at which data must be transferred in order for the
video to play smoothly without interruption. The data rate (also
called "bit rate") for a movie is measured in kilobytes
per second (K/s or KB/s). It can be calculated by dividing the size
of the file (in K) by the length of the movie (in seconds).
In the HTML 4.0 Specification, a label identifying an HTML tag or
attribute as "outdated" and discouraged from use in favor
of newer constructs (often style sheet controls).
and the Document Object Model. With DHTML, content can move across
the screen or respond to user inputs.
The approximation of a color by mixing pixels of similar colors that
are available in the image palette. The result of dithering is a
random dot pattern or noise in the image.
- Document Object Model (DOM)
The browser's internal hierarchical organization of the
elements in a document. The existence of a DOM makes page elements
available for manipulation via scripting or style sheets. Netscape
Navigator's and Microsoft Internet Explorer's DOMs differ
Dots per inch. In graphics, this is the measurement of the resolution
of a printed image. It is commonly (although incorrectly) used to
refer to the screen resolution of web graphics, which is technically
measured in ppi (pixels per inch). See also ppi.
Document Type Definition. A file associated with an SGML or XML
document that defines how the tags should be interpreted and
displayed by the application reading the document.
The process of converting an analog source (such as an analog audio
signal) into digital format. An encoder is the software that does the
- frame rate
In video, frames per second; used as a measure of video quality.
File Transfer Protocol. A protocol for moving files over the Internet
from one computer to another. FTP is a client/server system: one
machine must be running an FTP server, the other an FTP client.
Refers to the overall brightness of a computer monitor's
display. In technical terms, it is a numerical adjustment for the
nonlinear relationship of voltage to light intensity.
Graphic Interchange Format. Common file format of web graphic images.
GIF is a palette-based, 8-bit format that compresses images with the
lossless LZW compression scheme. GIF is most appropriate for images
with areas of flat color and sharp contrast. See also LZW
Handheld Device Markup Language. A specialized set of HTML tags for
creating documents to be displayed on handheld devices such as mobile
phones. It has been replaced by WML. See also
A base-16 numbering system consisting of the characters 0, 1, 2, 3,
4, 5, 6, 7, 8, 9, A, B, C, D, E, and F, where A through F represent
the decimal values 10 through 15. It is used in HTML for specifying
RGB color values.
Hypertext Markup Language. The format of web documents.
Hypertext Transfer Protocol. The protocol that defines how web pages
and media are requested and transferred between servers and browsers.
The W3C abbreviation for "Internationalization"
("i", 18 letters, then "n"), relating to
efforts to make the Web accessible in all languages.
A single image that contains multiple hypertext links.
- indexed color
In graphics, a system for rendering colors in 8-bit images. Indexed
color files, such as GIFs, contain an index (also called a palette or
color lookup table) of colors and associated index numbers, which is
used to render color in the image.
A cross-platform, object-oriented programming language developed by
Sun Microsystems. It can be used to create whole applications;
however, its primary contribution to the Web has been in the form of
Java applets, self-contained, mini-executable programs.
A client-side scripting language developed by Netscape that adds
interactivity and conditional behavior to web pages. It has little in
common with Java.
A lossy compression algorithm developed by the Joint Photographic
Experts Group. It is used by files in the JFIF format, which are
commonly referred to as "JPEG files." JPEG is most
efficient at compressing images with gradations in tone and no sharp
edge contrasts. Photographic images are typically best saved in JPEG
- key frames
In video, master frames placed throughout a video against which the
following frames are compared (for use with temporal, or interframe,
A version of Unix designed to run on PCs.
- lossy compression
A method for reducing file size in which some data (usually
indiscernible to human perception) is deleted in order to achieve a
higher compression rate.
- lossless compression
A method for reducing the size of a file without loss of data; in
lossless compression, redundant information is removed.
- LZW compression
Short for Lempel-Zev-Welch, the names of the inventors. A lossless
compression scheme that takes advantage of repetition in data streams
(such as a row of pixels of identical color). It is the compression
scheme used by graphic files in the GIF format.
Math Markup Language. An XML application for describing mathematical
notation and capturing its structure and content.
Musical Instrument Digital Interface. This audio format uses
numerical commands to describe the pitch and endurance of notes that
are "played" by available digital instrument sounds.
- MIME types
Multimedia Internet Mail Extensions. A protocol that defines a number
of content types and subtypes and allows programs like web browsers,
newsreaders, and email clients to recognize different kinds of files
and deal with them appropriately. The MIME type specifies what media
a file is, such as an image, audio, or video, and the subtype
identifies the precise file format.
Audio file format (MPEG I, Level-III) capable of high levels of
compression with little discernible loss of quality. It has become
the standard for sharing audio files over the Internet.
A family of multimedia standards created by the Motion Picture
Experts Group, commonly used to refer to audio and video files saved
using one of the MPEG compression schemes.
A uniquely named group of element and attribute names. XML documents
refer to namespaces in order to prevent confusion between competing
DTD tag names.
A table in an 8-bit indexed color file (such as GIF) that provides
color information for the pixels in the image. See also
Portable Document Format. A file format developed by Adobe Systems
used for capturing formatted page layouts for distribution. PDF
documents, when viewed with the required Adobe Acrobat Reader, will
appear exactly as they were intended.
Hypertext Preprocessor. An open source, server-side tool for creating
dynamically generated web pages (similar to Microsoft's ASP).
Portable Network Format. A versatile graphics file format that
features support for both 8-bit (PNG8) indexed images and 24-bit
images (PNG24). PNGs also feature variable transparency levels,
automatic color correction controls, and a lossless yet highly
efficient compression scheme.
Pixels per inch. The measurement of the resolution of a screen image.
A system extension that makes it possible to view audio and video
information on a computer. It was originally developed for the
Macintosh but is now available for Windows machines as well, and has
been adopted as the video standard by the ISO in their development of
MPEG-4. The term also refers to the file format.
Resource Description Framework. An XML application used to define the
structure of metadata for documents, i.e., data that is useful for
indexing, navigating, and searching a site.
Rich Music Format. A proprietary audio format used by the Beatnik
- resource fork
Extra code added in the Macintosh file format, used for storing
icons, previews, and file type information. This information should
be stripped out when sending the file to a non-Macintosh server. See
also data fork.
- RGB color
A color system that describes colors based on combinations of red,
green, and blue light.
The act of passing the mouse pointer over an element's space,
or the events triggered by that action (such as a changing graphic or
pop-up message, sometimes called rollover events).
- sampling rate
In a digital audio file, the number of samples taken per second.
A networked computer that provides some kind of service or
- Server Side Includes (SSI)
Special placeholders in an HTML document that the server is to
replace with actual data just before sending the final document to
the browser. Extended SSI (XSSI) (part of Apache 1.2 and higher)
provides more advanced command functions, including conditional
Standard Generalized Markup Language. A metalanguage that provides a
comprehensive set of syntax rules for marking up the structure of
documents and data. HTML is a subset of SGML.
Proprietary technology from Macromedia, Inc., for the web delivery of
Synchronized Multimedia Integration Language, an XML-based language
for creating multimedia, time-based presentation. SMIL combines
audio, video, text, animation, and graphics in a precise,
- spatial compression
In video, spatial compression is applied to each individual frame of
the video, using compression schemes commonly used on still images
(also called "intraframe" compression).
- spatial frequency
Refers to the concentration of detail in an image. For example, an
image of a blue sky would be considered to have low frequency. A
detailed image, such as a close-up of blades of grass, has high
Standardized Vector Graphics. A language for defining two-dimensional
vector graphics in XML.
An internet protocol for logging into and using a remote system on
the Internet. Telnet is a client/server system that requires a telnet
server running on one computer and a telnet client on the other.
- temporal compression
In video, temporal compression takes place over a series of frames,
deleting information that is repeated between frames (also called
A multiuser, multitasking operating system developed by Bell
Laboratories. It also provides programs for editing text, sending
email, preparing tables, performing calculations, and many other
specialized functions that normally require separate applications
- valid code
In an XML application, code that properly uses the elements and
attributes as specified in a Document Type Definition (DTD).
The World Wide Web Consortium. A consortium of many companies and
organizations that "exists to develop common standards for the
evolution of the World Wide Web." It is run by a joint effort
between the Laboratory for Computer Science at the Massachusetts
Institute of Technology and CERN, the European Particle Physics
Laboratory, where the WWW was first developed.
Web Accessibility Initiative. The committee at the World Wide Web
Consortium (W3C) that ensures that web technologies are accessible to
users with disabilities.
Wireless Application Protocol. A collection of standards and
specifications for delivering Internet-like information to wireless
devices such as mobile phones, pagers, PDAs, etc.
Waveform Audio File Format. This format was developed for the PC but
is now supported on Macintosh as well.
- Web Palette
The set of 216 colors that will not dither or shift when viewed with
browsers on 8-bit monitors.
- well-formed code
Code that abides by the strict syntax rules of XML.
Wireless Markup Language. An XML-based language for creating
applications for wireless devices. It is part of the Wireless
Application Protocol (WAP).
A reworking of the HTML 4.0 Specification to abide by the rules and
syntax of XML.
Extensible Markup Language. A new standard for marking up documents
and data. XML is based on SGML, but with a reduced feature set that
is more appropriate for distribution via the Web. XML allows authors
to create customized tag sets to provide functionality not available
Extensible Style Language. A system for controlling the presentation
of complex XML documents and structured data.
Extended SSI. See Server Side Includes.
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