The combination of the words "homo" and "brother"/"bro". Refers to acts that would typically be taken as gay between good friends.
However, there is still a line that can be crossed between homo and bromo. Bromo is acceptable; hugging your buddy is fine. Homo is not acceptable; whipping out your wang and letting your bro touch it is *not* bromo, that's just straight homo.
Typically the difference between bromo and homo is easily told apart in each scenario of the usage.
Guy 1: Dude! I haven't seen you in forever! *hugs bro*
Girlfriend: That's homo.
Guy 2: Nah, girl, 's all good. It's all bromo.