1) A khum is another word describing the male genitalia, also referred to as the penis, in a more comical way. Was used by Sacha Baren Cohen in the movie BORAT.
2) It can also be substituted for the word Fuck in some situations as well.
3) Khummy can also be used and it is used to describe when a person is feeling horny.
I have a very big Khum.(1)
You're such a khum. (1)
Shut the Khum up! (2)
I'm so khummy right now. (3)