The sudden, and often timely, understanding of a subject, usually in school. Most commonly paired with a loud exclamation of "OHHHHHHHHHHH! I GET IT NOW!" or something very similar. Usually done by the less studious members of the class, who understand it right before a test or quiz.
Teacher: So if you want to make x=2, you can. Just plug in 0 for y.
Student 1: OHHH! OH! OH! I GET IT NOW! So you just have to ...?
Teacher: Yes, Michelle, that's it. I've explained it for 3 weeks now."
Student 1: SWEET! I WILL SO ACE THIS QUIZ!
Student 2: Someone just had a braingasm...