Ent seems to be a term associated with treants. In Warcraft III, the Corrupted Treant, Poison Treant, and Plague Treant are called "corrupted ents". In WoW, the model that treants use is called "ent". A few treant mobs exist in WoW with the term "ent" in their name.
The animated gif from the website is called "corrupted ent".