Something that happens out of the norm, doesn't adhere to pattern, chaotic, nowadays a VERY overused and commonly misused word, making people like us who try to use it in it's true sense sound like teenage douchebags.
(retarded teenage use) We don't really need some random bass line in there.
#2 That shirt is totally random.
#3 Correct usage. "The word "random" should not be used randomly, you douchebag. Of course, you're so stupid you don't even know the definition, so why do I even try?"