An umbrella term is a word or phrase that covers a broad interval or set of functions or items that all fall under a single common category. For example, cryptology is an umbrella term that encompasses cryptography and cryptanalysis, among other fields. Similarly, an umbrella organization is a central and coordinating body representing a number of smaller, separate bodies.
The closely related blanket term is a word or phrase that is used to describe multiple groups of related things. The degree of relation may vary or have a minimal relationship, but blanket terms often trade specificity for ease-of-use; in other words, a blanket term by itself gives little detail about the things that it describes or the relationships between them, but is easy to say and remember. Blanket terms may originate as slang, and eventually become integrated into the general vocabulary.
Random House Webster's College Dictionary. New York: Random House. 1992.
Cascone, The Aesthetics of Failure "..an umbrella term for alternative, largely dance-based electronic music (including house, techno, electro, drum'n'bass, ambient).."