A fork of Rural Dictionary
The phrase is an intentionally misspelled "Oh hi" and is usually used as a title on cutesy pictures of animals like on lolcats. The phrase is often followed by a short, badly spelled sentence as if the animal/subject in the picture is talking to the viewer. O Hai may also refer to these types of cutsey animal images in general.
Picture of kitten in a stack of business reports. "O Hai, i am bein yur nu secritary. Get me cofy."
Another way of saying "Oh, Hey there!" As started on the freenode network channel #tyreus
Ambur has joined #tyreus <Brad_R> O hai thar, Ambur! <Ambur> O hai!