A super-strong or advanced pirate who protects lower-level pirates from larger enemies by engaging them first, so the lower levels can defeat high-level enemies and reap larger rewards. They may heal others as well.
Tanks enable these newer characters to level faster with a lower risk of being defeated easily by larger opponents.
To act as a tank and protect lower-level pirates from larger enemies by drawing the enemies attacks at themselves.
The AI in Pirates Online used to have enemies attack which pirate it saw first, but as of now they alternate between all pirates dealing damage to them - making tanking more difficult.