Technically it is audio data that is stored on a computer system, represented by a binary system (1's and 0's), and read by audio software. In layman's language it is music files that can be downloaded, played, and shared on any number of devices. On the Internet, music is digital and it comes in several file formats.
There are three major groups of audio file formats:
Uncompressed audio formats, such as WAV, AIF, and AU;
Lossless compression formats (which allows the exact original data to be reconstructed), such as FLAC, APE, WV, TTA, Apple Lossless, WMA; and
Lossy compression formats (which does not allow the exact original data to be reconstructed from the compressed data), such as MP3, AAC, lossy WMA.