A field of meta-data in MP3 and MP3pro audio files. The tags describe the contents, including song title, artist, album, year, comment, CD track and genre. ID3 tags are used for searching as well as displaying the title being played. In many cases, ID3 tags are not filled in or are erroneous, and an "ID3 tagger" utility, also called an "audio tagger" or "MP3 tagger," can be used to update them.

Other than MP3
Although often erroneously called ID3 tags, other audio files (AAC, WMA, Ogg Vorbis, etc.) have their own meta-data tag format, but hold the same kinds of data. See music search and MusicBrainz.

Why Was This Missing?
Music CDs evolved from phonograph records that contained only sound waves "carved" into the vinyl platters. Although reserving a few thousand bytes out of 650 million would have been easy, nobody envisioned playing a CD on the computer. Early CD players had only a few digits of display, which is why track number and length were the only meta-data in a CD; however, more description fields were later added (see CD Text).

ID3 Format
Version 2 of the format (ID3v2) supports variable-length fields that hold titles of any length as well as the album cover image. The tags are at the beginning of the file so that song information can be displayed at the start for streaming audio.

The original version of the format located the data in the last 128 bytes of the file and was limited to 30-byte text fields, a 4-byte year and 1-byte genre (80 categories). Version 1.1 (ID3v1.1) added CD track number. For more information, visit www.id3.org. See music CD identification, music search, metadata and streaming audio.