Ah! So good of you to ask. In an early episode it was revealed to stand for "Talmadge". Later, however, in one of the Star Trek movies, it was altered to "Tiberius", which is far more impressive, and shows the increasing sophistication of the whole Star Trek mentality from the "Gee Whiz!" days of the late 60's to the multi-cultural wonders of the later 20th century.

"James Tiberius Kirk"

Just saying it gives a person the shivers, eh? :-) You know them aliens ain't gonna get too far messing with this starship captain, specially not when his T-shirt gets half torn off and he really gets mad! By golly, soon Bones will have reason to say those deathless words:

"He's dead, Jim."

Music, please!

Daaaa-Da-Da-Da-Da-Dummmmmm Daaaa-Daaaaa-Da-Da-Da-Da-Dummmmmmm

And so on...

- LH