In the field of mathematics, j is a number that is closely related to i, the most famous imaginary number of all. Here's an example: i^2=-1, and j^2=1, however, j does not =1. In equations dealing with hypercomplex numbers and other highly complicated mathematical fields, j will sometimes be used to replace i for the sake of simplicity.

Next time some jackoff thinks he's hot shit and introduces Graham's number to your math class so that it looks like he's a real whiz, kick his phony ass with j (Number)! Who's the hot shit now, huh?

by Dr. Apocalypse November 2, 2012

Famous blooper by Sean "Day9" Plott, a Starcraft 2 caster. Happened in Episode #200 of his daily show, when talking about Ben being the first victim to a FFA-Alphabetical Kill funday monday.

I know you are probably angry with your mother, you probably go like: why don't you name me Zen, or Wen, or even like, the Number J

by ceejay33 July 25, 2011

Refers to a marijuana joint, it combines two slang terms for a joint. The "J" is obvious....a joint is also sometimes refered to as a number. Since J is a letter, not a number, only those in the know will understand.

by g-rock March 17, 2009