J. Random /J rand'm/ n.

[common; generalized from J. Random Hacker] Arbitrary; ordinary; any one; any old. `J. Random' is often prefixed to a noun to make a name out of it. It means roughly `some particular' or `any specific one'. "Would you let J. Random Loser marry your daughter?" The most common uses are `J. Random Hacker', `J. Random Loser', and `J. Random Nerd' ("Should J. Random Loser be allowed to gun down other people?"), but it can be used simply as an elaborate version of random in any sense.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.