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.

when you're hungover as shit after a spending a night drunk as a skunk

Another way of saying "Oh, hi."

A greeting that has its origins in what is arguably the worst movie of all time: The Room (2003). This phrase is said about fifty times in the movie by various actors to various other actors, and very often at random, inappropriate times.

a way of saying hello to a good friend, or a way to weird out an acquaintance.

A word used in conversations or online games - an alternative for "oh, hey" - but makes you sound even more fucking retarded.

The Literal meaning of Ohai is unclear, but Ohai means "place of the stone" and this name was in use for the area before the coal mining or town was established. It has been noted that Morley stream near the town was previously called Ohai It is likely that the area was originally named in relation to a Maori stone quarry that is nearby.