In computing, RAR is a proprietary file format for data compression and archiving.
The RAR file format was developed by Eugene Roshal (hence the name RAR: Roshal Archive), who was born on March 10, 1972 in Russia and graduated from Chelyabinsk Technical University. He also developed programs for packing and unpacking RAR files, originally for DOS, and later ported to other platforms. The encoder (the main Windows version known as WinRAR) is distributed as shareware, but Roshal has released the decoder's source code under a license that allows free distribution and modification, on condition that it is not reverse-engineered to build a compatible encoder. The current developer is Alexander Roshal. The encoding method is held to be proprietary, but compatible programs for decompression are available for several platforms, such as the open-source 7-Zip.
The file extension is .rar. The MIME-Type is application/x-rar-compressed.
You must have your copy of Windows mistakenly configured to open up RAR files in Winamp. You can fix this by opening My Computer, selecting Tools -> Folder Options -> File Types, scrolling down to the RAR file extension, and deleting the association with Winamp. Next time you try to open a RAR file, Windows should prompt you to look up a program to use open the file, and probably point you to a website where you can download an appropriate program.