Lossless compression
Compression that loses no data during the compression or decompression process. Lossless compression is commonly used for compressing executables or other files such as images (e.g. GIF and PNG) that requires all data within the file to function correctly.
Some music sharing services, such as Apple iTunes, are also offering a lossless compression format for sound downloads. Although the file size of each song is dramatically increased because of the amount of compression done, the songs will sound almost identical to the CD and much better than an MP3.
Also see: Compress, FLAC, Lossy compression, Sound definitions