Ass Fusion 

Fusion of such fine ass that it makes dividing by zero child's play.

Dat ass be so fine, I would like to perform ass fusion to make a child cry due to masses of asses.

Ass Fusion by Nigger Joel April 14, 2014

Ass Fusion 

The bonding or fusion of ass hair and underwear after an "accident". This occurs after sitting for a long time and the shit dries like glue. A rare experience, but can be very painful.

I had a bad ass fusion the other day when Delta lost my fucking luggage and I was stuck in the car.

Ass Fusion by climber clown August 6, 2015

asslusion 

An illusion of ass. When a girl's clothing makes it appear like she has a nice ass, but in reality there is nothing there.

also applicable to men

"Damn that girl got a fine booty!"
"Nah man, she flat. Them jeans just be givin her an asslusion."

asslusion by LewDaMan October 9, 2016

Optical Asslusion

When ones gluteus maximus appears to be rotund but when a closer look is taken, it is actually taking the affect of an ass but no ass is found until further investigation is taken and the ass begins much lower.

The "Optical Asslusion" Looks good from far, far from good.

Optical Asslusion by WAAAAAAAAAAAALT April 21, 2008