The act of boarding an enemy ship in Assassin's Creed IV Black Flag.
This is done by swinging across the gap between two ships on a rope, and must be done within very close proximity to an enemy ship in order to work.
Once you have boarded an enemy ship, you can mess with their infrastructure from the inside.
Killing soldiers onboard the ship, taking out the ship's captain, and destroying cannons and other weapons can give your ship the advantage.
The ships can also be looted for treasure, which can be kept, equipped or sold.