A male definition. Adding muscle mass or weight by going to the gym frequently and eating a high-protein diet.
Q: Dude, why are you eating so much meat?
A: I'm trying to bulk up.
by Stud April 11, 2005
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The art of eating a lot of food to gain muscle mass. This art form is commonly used by people who are overweight or obese as an excuse to eat a lot because they recently bought a gym membership.
"Dude isn't that your like 8th burrito? Your going to get fat."

"No dude it's alright, I'm bulking up. I'm going to need it later for when i work out"
by Kaistianity January 25, 2012
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The act of which someone of Bulky nature becomes enraged.
Watch it man, he's Bulking Up
by Petorius March 06, 2005
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