There is common terminology that links all MMOs.
AFK - Away from Keyboard
BBL - Be Back Later
BRB - Be Right Back
NPC - Non-player character. In some cases the these non-player characters might be attackable, in others the NPC might only be present and unable to be attacked, such as a merchant non-player character.
Ninja AFK - Going away from keyboard while in a group or raid, without telling anyone you are going to be AFK
Ninja Looter - A person who loots a mob or chest without asking and without sharing.