Show interest in their games: Ask them about the games they enjoy playing, their favorite characters, or any recent gaming achievements. This shows that you value their interests.
1-Up
An extra life
GG
Good game 
Glitches
A bug in the game that may give a player an advantage.
Grind
Completing repeated tasks to gain XP points
HP
Health/Hit Points: the measurement of how much life your character has left