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.