When the ass cheeks of a person no longer exist or for that matter curve inward creating a concave surface. Othewise known as a Cass= concave+ass. The opposite of convex.
She had such a flat ass that it had now turned into a Cass.

He had what you would call a Cass, the opposite of a bubble butt.
by WTDAUSA February 04, 2009
Top Definition
An absolute ally and all around rock. The kind of person you always know will be in your corner.
I know that cass will be there for me.
by renwick February 05, 2010
Cass is the girl you meet online and if you are really lucky you might meet her in real life. This girl is the girl that is so nice and she is always there to make you smile and laugh and all around feel happy even if it's been your worst day ever. She's so gorgeous and pretty and perfect even if she doesn't see it everyone else does. If you spend one night with this girl u will want to talk to her forever. If you become best friends with this person your life will change you guys will always talk which will make you very happy and sometimes you guys get into little fights but she will always forgive you because she is just that nice. You wish you could meet her in real life almost every day but I guess sometimes you have to wait. I really love this Cass person
Look at that girl over there she is so pretty! That must be Cass
by ILoveApples7746 June 07, 2016
1.Cold Ass. Being cold in the ass. If you are cold in the ass you dont care about something.

2.Youve just been outside and you have a cold ass.
John says: you mother just died
You say: im cass i didnt like her anyway
Bro i just went a walk and now im so cass i have to take a bath.
by Dr.Cushe January 21, 2011
Can't Actually Support Shit

Military test station refered to as "Big Blue", that constantly breaks and will break at the worst possible time and can never be fixed.
LCpl: Big Blue broke again.

Sgt: Damnit!! CASS is the biggest piece of shit ever, where's my RSTS bench?
by CST0D69 October 28, 2009
A person cappable of sensitive behaviour, often victim to cruel pranks,but usually very forgiving of the person.
"Did you ditch him at the mall?"
"Yah, but he won't care he's a Cass."
by Katamari February 19, 2007
1. A person, of ambiguous sex, who enjoys Science Fiction and Computers.

2. A person, generally a girl, who ends up in a common-law marriage with their college room mate.

3. Any person with a black soul and a love of hacking.
1. God, it's playing Dungeons and Dragons again. It's such a Cass.

2. Only a Cass would live with their college room mate for seven years.

3. OMG, John just changed my Myspace Profile. He's such a Cass!
by Entchen May 07, 2007
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