Definition of a Troll

As we move through this unit and I spend more and more time studying trolls, I still seem to be stuck on one rudimentary idea: what is a troll/what is trolling? I know this seems like an easy question, but I've come to understand that people's definition of a troll tend to vary. 

Here is the surprisingly legitimate definition of a troll from "Urban Dictionary":

One who purposely and deliberately (that purpose usually being self-amusement) starts an argument in a manner which attacks others on a forum without in any way listening to the arguments proposed by his or her peers. He will spark of such an argument via the use of ad hominem attacks (i.e. 'you're nothing but a fanboy' is a popular phrase) with no substance or relevence to back them up as well as straw man arguments, which he uses to simply avoid addressing the essence of the issue.

In this sense, I understand trolling. But what about when trolling becomes more than just "you're nothing but a fanboy" such as in Lindy West's or Zelda Williams' cases? Is this still considered trolling or is this a catchall term we've tacked on our most vengeful cyber bullies? I would assume that your average gaming trolls who's comebacks are usually "your mom" are slightly offended that they're being confused with the likes of seriously harmful cyber bullies. I'm not condoning this behavior but I definitely think that there is a hierarchy within the trolling community that needs to be more broadly recognized. With that being said, I tend to think of trolling similarly to our classmate Cristofer Trimble, as he posted somewhat of a class system for trolls in an earlier post ( I'd recommend checking that out if you're lost in the world of trolls like me).

What's your definition of trolling/trolls? Do you think there's a hierarchy or is a troll a troll no matter the severity?