Advanced Audio Coding (AAC) is a standardized audio encoding format that uses lossy compression. It is similar to the .MP3 format, but provides better sound quality at similar bitrates.

The AAC format is used by the Apple iTunes Store and is supported by the iPod and iPhone. It is also used by the Sony PlayStation 3, PSP, and recent Walkman devices.

While advanced audio coding files may use the ".aac" extension, AAC encoding may also be used within various container formats. These include .MP4, .M4A, .M4P, .M4R, and .M4V files.