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1.
Keefer is an adjective denoting high-quality. It is frequently used to decribe marijuana but can be used in other contexts as well.
Hey man, this weed is totally keefer.

Yo Caretto, that movie was pretty keefer.
by Lynchmob44 October 18, 2006
 
2.
A man/boy immersed in the party/drinking/weed-smoking atmosphere of highschool or college life who attends all of the parties and yet never touches any sort of drug, be it alcohol, weed, pills, etc.
-Joe! Quit being such a Keefer and take a hit off of this steamroller!

-Hey Keefer grow a pair and keg stand this shit!
by SpecialD January 17, 2009
 
3.
A guy who will flirt with anything with a vagina, but who will never make any effort to have more of a relationship than that.
1: Have you talked to that guy over there?

2: Yea, but he's a total keefer.
by DiabetesDominatrix February 20, 2011
 
4.
To hit an almost impossible, seemingly random, showstopper shot that devastates, destroys, demolishes, and demoralizes the opposition.
I keefers'd that chump kid in banana.
by holl@holl@ July 10, 2008
 
5.
A really cool black person.
yo Samuel L Jackson is a straight up Keefer!
by blastingdrummer June 19, 2009