1.NounAlternative form of fu: an administrative subdivision of imperial China; the capital of such divisions.
2.NounA metasyntactic variable used to represent an unspecified entity. If part of a series of such entities, it is often the first in the series, and followed immediately by bar.
"Suppose we have two objects, foo and bar."
3.NounAlternative letter-case form of Foo (“placeholder god”).
4.InterjectionExpression of disappointment or disgust.