Someone who causes dismay to someone on the internet that they don't even know, much less befrended on a site. They are most likely known to put lame or hurtful comments on someone's facebook, YouTube video (mainly videos in which the user is attempting something new like animation or clay mation), or anywhere you can openly post comments. Internet Trolls are known to also have nver contributed to the site they terrorize on and have a lame username. The best way to control the troll is to post a hurtful comment back or just delete, mark as spam, or report the comment.
Example of an Internet Troll #1
Puckerupbabii120: You need to drop dead. You guys look so retarded in this piece of shit you call a video.
Example of an Internet Troll #2
JesusSUX101: Do you really think that anyone cares about you? You gay dickhead.