Trolling is when you try to piss people off. Like posting a thread saying "I'm not sure if I'm going to get into med school... I only have a 3.85 GPA, 37 MCAT, both my parents are Harvard educated physicians, and I've only been shadowing and volunteering for the last 7 years. What should I do guys?"
Trolls when it comes to forums are people who browse through threads w/o posting.