What does being a 'troll' mean..?

so me and my "friend" been fighting lately because she accuses me of copying her? She accuses me of copying her because she thinks she owns the shoes Vans. And I came to school with Vans on and she calls me a copycat and a biter! I hear her call me a "troll" and I'm wondering what the he'll that is. so, what's a troll? not the mystical creature troll, but something else but idk what it is..