See ZIP file.

(1) A file that contains one or more files that have been compressed into the ZIP format. Also called a "ZIP archive," "zipped file" or "zipped archive," the ZIP algorithm is the most popular compression method in use.

Not Just the .ZIP Extension
ZIP files typically have a .zip extension, but there are other extensions in use. For example, files with the .gz extension are actually zipped files and can be "unzipped" by any UnZip utility program. In the Java world, a JAR file is a ZIP file, but uses a .jar extension. Office Open XML, the default format in Microsoft Office 2007, is a ZIP file, and Word 2007 uses the .docx extension. Extensions such as .jar and .docx are used to wrap up a collection of files for a particular purpose so they can be easily identified and transported as a single entity. Nonetheless, in structure, they are all ZIP files.

ZIP From PKZIP
In the 1980s, Phil Katz developed algorithms for compressing files into smaller amounts of space, and his programs became PKZIP and PKUNZIP from PKWARE, Inc. The format became so popular that other companies such as Nico Mac and Netzip developed Zip and UnZip utilities, and the Zip/Unzip algorithms have been placed in the public domain. See PK software and WinZip.

(2) A file on a Zip disk. See Zip disk.