Misspelling of "human".
The misspelling is commonly attributed to those having Down Syndrome, especially in acute cases of it.
Corky: "I love the uman race!"
Corky's Mom: "Sweetie, the first letter of the word 'human' is 'h'! Here, let me grab your elmet, I mean helmet, for you."
A young guy who is a complete retard
Saidul: Uman where is your wheelchair?
Uman: I dunno