An interjection used to call someone's attention — "hey!" — often informal, brusque, and masculine.
おい、ちょっと待て！
Hey, wait a minute!
おい、そこの荷物をどけてくれ。
Hey, move that luggage over there.
おい、何してるんだよ！
Oi, what are you doing?!
A Kansai-dialect first-person pronoun meaning "I" or "me".
おいはもう帰るわ。
I'm going home already. (Kansai dialect)
おいがやったんやで、信じてや。
I did it, you know — believe me. (Kansai dialect)