Tank:

A tank is a hero or role built to absorb damage and draw attention from the enemy team. In Dota 2, tanks usually have high health, armor, and durability, and they often start fights, stand in front of allies, or soak spells while teammates deal damage.

The term is informal and describes a team function rather than a fixed hero class. A tank may also provide control or initiation, but the main idea is survivability and front-line presence.

Related: Initiator, Support