oi = hey/hi = cockney = east-london accent (UK)

a weird exclamtion.

a type of harsh, aggressive punk music originally popular in the late 1970s and early 1980s

"Oi" is a British version of "Hey", also a music style.
In Portuguese, Oi means "Hi". Maybe Britain get the accent of the Portuguese while they saved them for the Spanish king.
Oi is used(used to call someone, or to say "hi" in other version) in Australia,America,Canada, and, duh, Portuguese countries.
Many people in North America(Yep, Mexico and Greenland count) says "oi" as a natural part of their language or to do the same thing we do.

Also, Japanese for "hey".

An Australian way of getting someones attention, or if they bump into you or some shit like that.

"Hey"