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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
freedom of speech
The man is FOS (original meaning) ... he does not deserve the FOS.
by MIT-GUY August 11, 2012
Fortress of Solitude
When the freak from down the street came over for dinner, I retreated to my FOS.
by Mai327 May 15, 2011
Short for "Full Of Shitness"

A serious condition in which a person chooses a malady to be a victim of. This malady is usually vague, chronic and untreatable such as a "bad knee."

F.O.S. will tend to flare up when the person is confronted with a situation they would rather avoid.
"Is Robbie coming to your birthday party today?"

"No, she texted me yesterday. Apparently her F.O.S. is acting up, making it impossible for her to walk on her bad knee."
by mizJD January 10, 2010
Flowers over snitchs, found in a lil wayne song
F.O.S. for life!
F.O.S. all day
by BALLIN!! December 12, 2007
Fuck On Sight. An acronym used by two friends to describe a person who they see who they would like to instantly fornicate with on sight.
Two guys are walking when they see a really hot gurl and one gay says to another FOS? And the other gentleman nods in unison.
by Ilovecurry April 14, 2010
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