"Bro" is a word short for "brother". But some people may call their friends bro too.
Person 1: Hey my bro
Person 2: stop calling me that idiot.
youre bestie 4 ever and you need to tell them something NOW
BRO HELP MY TEACHER FAILED ME
A reasonable sign that the straight guy you have a crush on is not into you like that.
Gay guy: says anything to get his attention
Hottie: “yeah bro.”