Coolant tank
A coolant tank was a containment unit to store gases or liquids such as plasma coolant, used to cool parts of a starship or any vessel or base whose power generation units created extreme excess heat that could damage or destroy nearby components or structures. 

The  had coolant tanks on the left and right sides of the warp core. One tank was punctured by Data in a final blow to the Borg Queen. ()

Spacecraft components