abbreviation for "good game". depending on the context in which it is used it is either a compliment or a salty, halfassed insult. also can be said as "gfg" (good fucking game) when extremes of the matter are in question.
(polite)gg my friend, that was an exciting, exilirating game!!
(insulting)gg ogl scurb gtfo stfu an get soem skillz joo nubcake