Shield

Were you referring to:
 * Energy Shields, a technology utilised by both Covenant and UNSC supersoldiers which provides limited protection.
 * Shield Generator (Covenant), the Covenant structure which provides limited protection in Halo Wars.
 * Stationary Shield Generator, the device used by the Covenant during offensive ground operations.
 * MJOLNIR Shield Tester, a machine which generates the MJOLNIR's shield system.
 * Bubble Shield, a UNSC personal defence device.
 * Deployable Cover, a Halo 3 deployable piece of Equipment similar to the Stationary Shield Generator.
 * Shield Door, a Forerunner energy shield which only repels gunfire.