It's simply a form of expression to a lot of people. It means whatever the Fuck you want it to mean. It's a dynamic mathaFacka as you'll see below. It'll help get you through them days when you only have a two-page dictionary in your buffer. Use it to fill in those empty spaces in your daily conversation like you hear people do with the word Fuck, but with more of a street-like twist.
It's a verb,
it's a noun,
it's a mathaFacka
Comedian Bernie Mac said it best..
"I'm gonna break down what the word 'mathaFacka' actually means. It's about expression. Don't be ashamed of the word 'mathaFacka,' 'cause the word 'mathaFacka' is a noun. It describes a person, place or thing. It's just expression. You might see three or four brothers together. You might hear the word 'mathaFacka' 32 times. And you might hear just two regular English words. But the conversation makes sense like a mathaFacka. Everybody can understand it. Don't be afraid of the word 'mathaFacka.' I'm gonna break it down to you. If you out there this afternoon and you see about three or four brothers talkin, you might hear a conversation, and it go like this:
'You seen that mathaFackin Bobby?
That mathaFacka owe me 35 mathaFackin dollars. He told me he gonna pay my mathaFackin money last mathaFackin week. I ain't seen this mathaFacka yet.
I'm not gonna chase this mathaFacka for my 35 mathaFackin dollars. I called the mathaFacka four mathaFackin times, but the mathaFacka won't call me back. I called his mama the other mathaFackin day.
She gonna play like the mathaFacka weren't in. I started to cuss her mathaFackin ass out, but I didn't want no mathaFackin trouble. But I'll tell you one mathaFackin thing.
The next mathaFackin time I see this mathaFacka, and he ain't got my mathaFackin money, I'm gonna bust
his mathaFackin head!'
..and I'm out this mathaFacka."
A quick, nice, and lazy way of calling your boy an Asshole while asking him "What's up?"
What's up, Asshole?
Hey, so what's up, Asshole?
Aye, so what's up?
Ayeso, what's up? (sentence structure inverts into...)
What's up, Ayeso?
"Not much, Ayeso"