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1.
a fancy word for shit
I just did a huge biomass at the National Gallery toilet.
by P3 EDay 2 April 28, 2010
 
2.
Used in two forms, the former used more popularly;

1. Kg/m^2 of living materials in an ecosystem

2. Mob of people, population
Dude, look at that huge biomass of mutant radioactive zombies!
by suicidoll June 04, 2006