Definition:
A firm album is an album a record label has contractually committed to releasing. When you sign a record deal, your first album is usually the only firm album included in the deal, though the label will often retain "options" for future releases. Options do not commit a label to releasing a record by you but rather gives them first dibs on your new music.
Although deals including one firm album are most common, you may encounter deals that include two or more firm albums.
