The ZIP file format is a popular lossless data compression and
archival format. A ZIP file contains one or more files that have been
compressed, to reduce their file size, or stored as-is. A number of
compression algorithms are permitted in zip files but as of 2008 only
DEFLATE is widely used and supported. 

The format was originally evolved by Phil Katz for PKZIP from the
previous ARC compression format by Thom Henderson. However, many
software utilities other than PKZIP itself are now available to
create, modify, or open (unzip, decompress) ZIP files, notably WinZip,
BOMArchiveHelper, KGB Archiver, PicoZip, Info-ZIP, WinRAR, IZArc,
7-Zip, ALZip, TUGZip, PeaZip, Universal Extractor and Zip
Genius. Microsoft has included built-in ZIP support (under the name
"compressed folders") in later versions of its Windows operating
system. Apple has included built-in ZIP support in Mac OS X 10.3 and
later via the BOMArchiveHelper utility. 

ZIP files generally use the file extensions ".zip" or ".ZIP" and the
MIME media type application/zip. Some software uses the ZIP file
format as a wrapper for a large number of small items in a specific
structure. Generally when this is done a different file extension is
used. Examples of this usage are Java JAR files, id Software .pk3/.pk4
files, package files for StepMania and Winamp/Windows Media Player
skins, XPInstall, as well as OpenDocument and Office Open XML office
formats. Both OpenDocument and Office Open XML formats use the JAR
file format internally, so files can be easily uncompressed and
compressed using tools for ZIP files. Google Earth makes use of KMZ
files, which are just KML files in ZIP format. Mozilla Firefox Add-ons
are zip files with extension "xpi". Nokia's mobile phone themes are
zipped with extension "nth".
