Biome - Type of realm area. Badlands, Grasslands, or Swamp.
Hive - A group of players' cities arranged close together. Clans commonly create a "hive" for ease of sending goods, defending, and increased chance of spawning nearby titans.
OC - Over Cap. Resources in excess of your Protected Cap, and therefore vulnerable to being looted after a successful enemy attack.
Rein - Reinforce, sending troops to defend another city.
RSS - Resources.
Snipe - To take the last hit and destroy a realm monster or titan that another player has been attacking. Can sometimes be applied to quests as well: to take first place in the final seconds of a quest.
Spawn - New monsters, titans, or resource nodes appearing on the map. Monsters and resources get a shield which prevents players from interacting with them for a short time after appearing.
TH - Town Hall. e.g. TH12 is Town Hall Level 12.
UC - Under Cap. Being under the Protected Cap, and therefore not at risk of being looted.
Zero - A barrage of attacks that fills a player's hospital and kills all troops in excess of their hospital capacity.