Were I to do so, someone else would probably alter the fruit of all my labour - life's too short :-)

But I would not try to do so, as it is far easier to see what is wrong with attempted definitions of such terms, than provide an adequate general definition. This is because they have been developed by various people in different contexts with somewhat different views. Cf.

The phrase was originally coined as "Trolling for flames", where the posters intention was to incite a "flame war", the Usenet intellectual equivalent of a bar fight.

But it can vary, some variants being quite harmless, others not:

 Many trolls are just practical jokers attempting to amuse themselves and their audience. Some have genuine animosity toward a particular group or individual that they believe has done them wrong. Some are just loathsome, contemptible hooligans bent on disrupting the ordinarily peaceful exchange of useful information for their own perverted pleasure.

http://groups.google.com/group/alt.troll/msg/bc2e71e19c590d8e