An MP3 file is a type of audio file that uses a compression algorithm to reduce the overall file size. It is a commonly distributed audio file used today and is known as a "lossy" format because some of the sources original data is lost during the compression. MP3 files can be opened and played on devices capable of decoding and playing them. In the context of the search results, "What It Is" is a song by Doechii, a hip hop artist, and is available for download in MP3 format.