Short for Advanced Audio Coding.
AAC is a file format for music and other audio content. It is commonly used on the Internet, on PCs, and on portable devices, including dedicated music players and phones with music player functionality.
AAC is a newer alternative to MP3. Compared to MP3, AAC is designed to have better sound quality with smaller file sizes (requiring less memory).
AAC is also designed to work with DRM technologies that control how the music files can be played and/or shared to enforce copyrights.
Newer and better versions include AAC+ and AAC++.