1. short for "organic chemistry."
2. an extremely difficult course that one takes, usually during the second year of college for prospective Pre-Med students. It is associated as a "weeder" class for hopeful students, as many people drop the class before they complete it.
"Holy fuck man, I don't get any of this orgo stuff at all."
"I want to drop this class, but I don't wanna look like a fucking retard. What should I do?"
"Idk man. Idk."