this is a shorter term for "Flap Of Skin". a flap of skin is someone in your group of friends whom you may consider the "loser" or the person who you only hang around with for a certain reason, that reason not perticulary meaning you enjoy their company.

it could also mean someone with NO private parts.
" Kris has no vagina"

"She is but a Flap Of Skin!"

"I couldn't concentrate when the FOS was talking to me, she annoys me to much."
by i heart flap of skin July 12, 2009
Top Definition
Abbrev. Full of shit.
by Targen December 02, 2002
An abbreviation, meaning "fuckable-on-site". Used to classify extremely sexy people who arouse others to an immediate, uncontrollable frenzy.
Jared Leto (of 30stm) - inherently FOS. No question.
by _Jules_ December 17, 2008
The acronym for a person who is Full of Shit. When someone is constantly telling outrageous lies, typically about themself, in order to impress others.
"Did you hear that FOS was offered a full scholarship to Harvard, but turned it down to be a UPS driver?"
by Quinn Littles May 14, 2009
Abreviation for "Full of Shit"
You are so "F.O.S."
They are really so "F.O.S."
by Bev Lane May 29, 2006
Full of shit
Never trust a used-car salesman, they're all FOS.
by Barbarella11 December 20, 2010
Code word for full of shit to get you out of trouble. You say it to someone and they just look confused when other people might realize what it means. Can also be pronounced Fos for short.
When my teacher told me that my homework assignment I turned in was worth a D when I knew it was worth and A, I said "You're F.O.S., this work is flawless!" I got sent to the office because apparently he knew what F.O.S. meant.
by PrincessR December 06, 2009
Abbreviation: FOS = Full of Shit

• It can mean that someone is lying, therefore full of shit.

• It can also mean the literal aspect, the state of being FOS.
(constipated) or (bowel obstruction)
That patient is totally FOS, just trying to get some drugs.

The patient in room 22 is literally FOS; constipated as hell.

They tried to tell me a BS story about losing their prescription, but I can tell they are FOS.
by Night.ER.Ninja July 27, 2014

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