A word used to express emotions of a variety of sort, such as anger, confusion, contentment, and so on. It depends upon the tone of voice and context to determine the specific use of the word. Most often used (and originally used by James T. Kirk) to express rage, when it is drawn out.
Anger/Rage: Person A: I got a parking ticket!? KHAAAAAAN!
Confusion/: (A clown on fire runs past singing Christmas carols) Person B: . . . Khan?
Content: (Finishes eating delicious cake) Person C: Ahhhh. Khaaan.
Shock/Surprise: (A ghost appears) Person D: KHAN!?