ST Shields

Most starships in Star Trek use defensive shield technology to protect against enemy attacks. As the shields take damage, they become weakened and effects from enemy attacks bleed through with greater frequency.

Nature

Shields are usually depicted as a bubble surrounding a starship that is visible only when actively resisting an attack. During the Dominion War, shields seemed to conform to the hulls of the starships projecting them.

Most transporters cannot beam through combat-grade defensive shields.

Capability

Standard Shields: These are the standard shields used by most starships. High Capacity Shields: These are used on the Galaxy-class. Their name suggests that they can take one hell of a beating. Regerative Shields: These shields are a new type seen on the Prometheus Class. They might also be on the Sovereign Class. As its name suggests, it probably regenerates quite quickly during combat.