1: Verb; You and, your friends are in an apocalyptic world (in reference to a zombie apocalypse). Everyone gets along well, hence the 'bro' in Zombro.
2:Noun; A group of mindless bros, typically as far as the eye can see.
3:Adjective; to describe a situation in which, you must rely on your 'bros' to pass.
1; " Dude, this Zombro Apocalypse is awful. No running water really kills me. Literally."
2; "Hey watch it! A Zombro Apocalypse started at that new Ice cream shop. Take my frisbee, use it wisely."
3; "This test is going to be a Zombro Apocalypse. I'll help you, if you help me."