See also BoxSetNameStyle, an official style guideline.

Many releases come in boxed sets; sometimes they are available only in a boxed set, like a 2 disc compilation or an artist anthology or:

• (a) Sometimes they are available either in a boxed set or not, like a singles collection boxed set
• (b) Sometimes the first disc is a normal release, and other discs are bonus discs only available with certain special releases etc.
• (c) Sometimes they are only available singly, but they are related in a set somehow, like more than one soundtrack album for a film or a single having a disc 2
• (d) a series of compilations.