Advanced Audio Coding (AAC) is a digital audio format known for its high compression efficiency and better sound quality compared to MP3 at similar bit rates. It's widely used in streaming, broadcasting, and as the default audio format for Apple's iTunes and devices.

AAC was developed in 1997 as part of the MPEG-2 standard and later enhanced in the MPEG-4 standard. It was created by a collaboration of companies including Fraunhofer IIS, AT&T, Dolby, and Sony, aiming to provide better sound quality than MP3 at similar bit rates. AAC gained significant popularity with the advent of Apple's iTunes in 2003, which adopted the format as its default audio codec. This widespread usage was further bolstered by its inclusion in many streaming services, digital radios, and mobile devices. Today, AAC is a versatile and widely-used format, known for its efficiency in compressing audio while maintaining high quality.