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   Zip is a file format used for data compression and archiving. A zip file contains one or more files that have been compressed, to reduce file size, or stored as is. The zip file format permits a number of compression algorithms. The format was originally created in 1989 by Phil Katz, and was first implemented in PKWARE's PKZIP utility,[2] as a replacement for the previous ARC compression format by Thom Henderson. The zip format is now supported by many software utilities other than PKZIP. Microsoft has included built-in zip support (under the name "compressed folders") in versions of Microsoft Windows since 1998. Apple has included built-in zip support in Mac OS X 10.3 (via BOMArchiveHelper, now Archive Utility) and later.

http://en.wikipedia.org/wiki/Zip_%28file_format%29

Zip files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip.[1] Zip is used as a base file format by many programs, usually under a different name. Zip files are often represented by a document or other object prominently featuring a zipper.