Fo can mean the following
1. Slang for the number "four"

2. Slang for "for"

3. Slang for info, or information
1. Yo, gimme the fo discs

2. Fo Shizzle (For sure)

3. Gimme the fo on dat guy.
by AnnoyedBlackGuy August 10, 2006
the number between 3 and 5
I axed my moms for fo dollas
by Vegas March 24, 2003
Abbreviation of Fuck off
Guy one: I don't like you
Guy two: FO
by 2451346523562 December 24, 2010
reffering to the number "four".
reffering to the word "for".
"Im fo dollas short on my bill dawg"
"Fo sho my niggas"
"Im all fo you baby"
"One, Two, Three, Fo"
"Fo real"
by ShOvel July 24, 2003
'Fuck off', abbreviated for use in chatrooms, email or text meassages.
'Fuck', taken from 'mofo', which in turn is an abbreviation of 'motherfucker'.
'For', most common used in the phrase 'fo sure'/ 'fo shizzle', both meaning 'for sure', a complicated way of saying 'yes'.
-fo u gay
-Shaddup, you fo!
-Fo shizzle my nizzle...
by Duff November 20, 2004
Nathan Fillion created the acronym FO, which is the short form for his phrase Full On. It can be used on its own, and/or to intensify a phrase, such as Double Rainbow.

It means that which is:

•fully ecstatically wondrous

•beyond joyfully amazing

•intensely orgasmically blissful
Here are some usage examples for FO, which is short for Full On. (For more examples, see the Twitter page belonging to NathanFillion:)

Nathan Fillion, on his Twitter page, kindly acknowledged my entry work defining his recommendation of the new "in" phrase: "Double Rainbow" on Urban Dictionary! He said it is "Full on." Thank you, Nathan. You are so Full On Double Rainbow! (FO DR!)

The TV shows Castle and Firefly are so intense, they are Full On Double Rainbow! (FO DR!)

Serenity, the feature film starring Nathan Fillion, is so vivid, it's Full On Double Rainbow! (FO DR!)

Nathan Fillion is so awesomely spectacular, sexyhotmessgorgeous, and brilliantly talented, his fame is sweeping across the nation, and over all the world! He is Nathan "Full On" Fillion!
by Kcat10 August 01, 2010
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