Resting in order to gain back mana in EQ was called Meditating. This is the commonly used abbreviation, also shortened to Med, as in, "Don't pull yet, I need to med."
Massively multiplayer online role-playing game (commonly abbreviated MMORPG) is a genre of computer role-playing games in which a large number of players interact with one another within a virtual game world. The term MMORPG was coined by Richard Garriott,the creator of Ultima Online, the game credited with popularizing the genre in 1997.
MOB is an old programming acronym of Mobile Object Block. Mobs are all computer controlled characters in the game. You should likely use some other term such as monster, creep, or bad guy.
Multi User Domains / Dungeons. A Digital Realm where contains multiple players / people.