Distinctive titles are titles that are unique — for example, there's only one Firebird by Stravinsky. However, the title appears in its original language. So Firebird appears as Zhar-ptitsa. Other examples:
Form titles use the common genre names familiar to most musicians — particularly with instrumental music — like sonatas, masses, quartets, etc.
Form titles have several common pieces:
Here are a couple of examples:
"Extra information" can be used for a variety of useful bits of information. For example:
A musical work might be known by many different titles.
A uniform title (or preferred title) is the version of a title standardized by catalogers. Books, scores, and recordings of a particular musical work can be searched more quickly by searching by uniform title.
Uniform titles come in two flavors: Distinctive titles and form titles.
Uniform titles can also be used to show groups of pieces put together in a published work (like 3 sonatas in one volume). Examples:
That last one is important. If we have a complete works edition of a given composer, you'll find it listed under "Works." The same would be used for an edition of CDs of every single work by a given composer.