1. <tool, compression, file format> A compressed archive containing one or more files, the act of creating it and its filename extension. Originally, such a "zip file" was created using PKWare, Inc.'s PKZIP utility program for MS-DOS.
Due to the popularity of the original program, the format has spread to Windows, Unix and other operating systems and the function is often built into file managers.
unzip is the corresponding de-archiver or the act of extracting files from an archive.
The first two bytes of a zip file are the ASCII characters "PK" after Phil Katz who developed the original PKZIP.
See also gzip, tar and feather.