Vessel is an unoccupied body or cadaver, which can be possessed by the player and then becomes an Avatar. There only can be one vessel possessed at a time, but one can own more than one vessel. Unpossessed vessels are like any other inventory object. Vessels can be collected, traded and crafted, too.
New vessels can also be found during campaigns (on graveyards) and since they are like any other item, they are subject to inventory capacities and embargo rules.
If players allow their vessel to be destroyed, they will lose any applied discipline runestones.
Avatars can leave a vessel either per death or voluntarily.