The nickname a user has chosen to be identified by when playing Internet games.
Graymail refers to unwanted email messages that do not otherwise meet the criteria of spam. Typically, graymail consists of emails from entities with whom the user has registered or signed up for regular email notifications. Graymail often includes newsletters, mailing lists and membership announcements, and forum updates.
Internet gamers that intentionally cause problems or cyberbully other gamers.
This refers to techniques by sexual predators to get to know and seduce their victims in preparation for sexual abuse.
GTG means Got to go.