Ancient creeps:

Ancient creeps are strong neutral units found in special jungle camps that are tougher and more rewarding than regular neutral creeps. They are commonly farmed for gold and experience once a hero can clear them efficiently.

Because Ancient camps usually take longer to kill, they are often targeted by heroes with strong area damage, summons, or scaling damage. The term also appears in strategies and map calls when players refer to Ancient camp stacking, clearing, or blocking.

Related: Neutral creeps, Jungle, Farming