\Fum\, v. i.
To play upon a fiddle. [Obs.]
Follow me, and fum as you go. --B. Jonson.
Computing Dictionary
Definition:
[XEROX PARC] At PARC, often the third of the standard metasyntactic variables (after foo and bar). Competes with baz, which is more common outside PARC.
Webster's 1913 Dictionary