RAR

RAR stands for Roshal ARchive. It is a proprietary^[2] archive file format that supports data compression, error recovery, and file spanning. It was developed by a Russian software engineer, Eugene Roshal (the first letter of his surname contributing to the name of the archive format), and is currently licensed by win.rar GmbH.^[3]
The filename extension used by RAR is .rar for the data volume set and .rev for the recovery volume set. In previous versions, if a RAR-archive was split into many smaller files (a "multi-volume archive"), the smaller files used the extensions .rar, .r00, .r01, .r02 etc.

Version 1 and 2 archive files were often used in conjunction with a parchive file archiver to create parity files for error recovery when using less-than-perfect file transmission and storage media such as newsgroups, satellite transmission, and optical discs. Version 3 has eliminated the need for third party post-processing.

source: www.wikipedia.com