The type of a release group describes what kind of release group it is. It is divided in two: a release group can have a "main" type and an unspecified number of extra types.
An album, perhaps better defined as a "Long Play" (LP) release, generally consists of previously unreleased material (unless this type is combined with secondary types which change that, such as "Compilation").
A single has different definitions depending on the market it is released for.
- In the US market, a single typically has one main song and possibly a handful of additional tracks or remixes of the main track; the single is usually named after its main song; the single is primarily released to get radio play and to promote release sales.
- The U.K. market (also Australia and Europe) is similar to the US market, however singles are often released as a two disc set, with each disc sold separately. They also sometimes have a longer version of the single (often combining the tracks from the two disc version) which is very similar to the US style single, and this is referred to as a "maxi-single". (In some cases the maxi-single is longer than the release the single comes from!)
- The Japanese market is much more single driven. The defining factor is typically the length of the single and the price it is sold at. Up until 1995 it was common that these singles would be released using a mini-cd format, which is basically a much smaller CD typically 8 cm in diameter. Around 1995 the 8cm single was phased out, and the standard 12cm CD single is more common now; generally re-releases of singles from pre-1995 will be released on the 12cm format, even if they were originally released on the 8cm format. Japanese singles often come with instrumental versions of the songs and also have maxi-singles like the UK with remixed versions of the songs. Sometimes a maxi-single will have more tracks than an EP but as it's all alternate versions of the same 2-3 songs it is still classified as a single.
There are other variations of the single called a "split single" where songs by two different artists are released on the one disc, typically vinyl. The term "B-Side" comes from the era when singles were released on 7 inch (or sometimes 12 inch) vinyl with a song on each side, and so side A is the track that the single is named for, and the other side - side B - would contain a bonus song, or sometimes even the same song.
An EP is a so-called "Extended Play" release and often contains the letters EP in the title. Generally an EP will be shorter than a full length release (an LP or "Long Play") and the tracks are usually exclusive to the EP, in other words the tracks don't come from a previously issued release. EP is fairly difficult to define; usually it should only be assumed that a release is an EP if the artist defines it as such.
A Mini-Album (or Mini-LP) is a release that is in between EP and Album in terms of number of tracks and length. The number of tracks is around 7-9, and the length varies from around 20-35 mins. There is no strict definition along these terms, as many EPs and Albums fit these criteria. What is important is that the artist or label consistently refers to the release as a Mini-Album. Where this is not the case, notably where Mini-Album and EP are used interchangeably, EP should be used.
An episodic release that was originally broadcast via radio, television, or the Internet, including podcasts.
Any release that does not fit or can't decisively be placed in any of the categories above.
A compilation, for the purposes of the MusicBrainz database, covers the following types of releases:
- an anthology, which is defined as being a group of songs from various sources combined together as a "best of" or retrospective type release.
- a various artists song collection, usually based on a general theme ("Songs for Lovers"), a particular year ("Hits of 1998"), or some other kind of grouping ("Songs From the Movies", the "Café del Mar" series, etc).
The MusicBrainz project does not generally consider the following to be compilations:
- a reissue of an album, even if it includes bonus tracks.
- a tribute release containing covers of another artists work.
- a classical release containing new recordings of a classical artists work.
- a release containing two albums and/or EPs (these should be tagged as either an 'album' or an 'EP' depending on the circumstances).
Note that there is a certain amount of crossover within the definition of compilation and the other types of release, for example a various artists soundtrack could also be considered a compilation. In general, compilation should be superseded by other release attributes when required.
A soundtrack is the musical score to a movie, TV series, stage show, computer game etc. In the specific cases of computer games, a game CD with audio tracks should be classified as a soundtrack: the musical properties of the CD are more interesting to MusicBrainz than the data properties.
Non-music spoken word releases.
An interview release contains an interview, generally with an Artist.
An audiobook is a book read by a narrator without music.
A release that was recorded live.
A release that primarily contains remixed material.
A DJ-mix is a sequence of several recordings played one after the other, each one modified so that they blend together into a continuous flow of music. A DJ mix release requires that the recordings be modified in some manner, and the DJ who does this modification is usually (although not always) credited in a fairly prominent way.
Promotional in nature (but not necessarily free), mixtapes and street albums are often released by artists to promote new artists, or upcoming studio albums by prominent artists. They are also sometimes used to keep fans' attention between studio releases and are most common in rap & hip hop genres. They are often not sanctioned by the artist's label, may lack proper sample or song clearances and vary widely in production and recording quality. While mixtapes are generally DJ-mixed, they are distinct from commercial DJ mixes (which are usually deemed compilations) and are defined by having a significant proportion of new material, including original production or original vocals over top of other artists' instrumentals. They are distinct from demos in that they are designed for release directly to the public and fans; not to labels.