Definition of troll noun from the Oxford Advanced Learner's Dictionary

troll

noun

trɒl

trəʊl

troʊl

1 (in Scandinavian stories) a creature that looks like an ugly person. Some trolls are very large and evil, others are small and friendly but like to trick people.2 (informal) a message to a discussion group on the Internet that somebody deliberately sends to make other people angry; a person who sends a message like this