A combination of Mace Windu and Dude!
It is a word that guys who are good friends (bros) can use to refer to one another. It can be used at basically any time. It does not have to be used in a Star Wars context, although it helps if all the bros are familiar with the Star Wars movies.
Guy1: Hey, whats up Mace Windude?
Guy2: Nothin much, bro, just gunna watch Star Wars Saturday on Spike TV today.
Guy1: Whoa brah, me too.