What do all the abbreviations ('lol, SL)' mean?

lol = 'laughing out loud', SL = 'Storyline,' TT = 'Tabletop' usually in reference to Tabletop roleplaying, afk = 'away from keyboard,' ttyl = 'talk to you later,' 'PC = Player Character,' NPC = 'Non-Player Character,' ST = 'Storyteller.' If someone uses something you're not familiar with, ask them.