In MusicBrainzTerminology, a release is an entry in the album table of the database. For CD's, a release represents 1 CD. For vinyl and cassettes, a release represents both sides of a record or cassette.
A release has a ReleaseTitle and consists of one or more Tracks. Each release has one ReleaseArtist who is the PrimaryArtist associated with that release. Other artists can be associated with a release using AdvancedRelationships.
A release has a ReleaseID, a unique identifier for that Release.