An expression made by cleverly switching the words "it" and "is" to create a grammatically nonsensical phrase meaning "What is it?". See "what up" or "aks" for similar constructions (or deconstructions depending on how you look at it).
What it is hoe, ah what's up (what's up)
Can a nigga get in them guts (them guts)
Cut you up like you ain't been cut (been cut) Show your ass how to really catch a nut (oh yeah yeah)
Well give me you number and I'll call (I'll call)
And I'll follow that ass in the mall (in the mall)
Take you home, let you juggle my balls (my balls)
While I'm beatin and tearin down your walls (oh yeah)
An all but lost phrase from the seventies era of ebonics, the closest contemporary equivalent being, "What up?" WHAT IT IS is often a rhetorical question like, "How's it hanging?" or "What's going on?"