RF Shields
RF shields are components which are used to absorb/dissipate RF noise/emissions. They are used both to protect sensitive circuits from external noise and to reduce the emissions of noisy circuits.
Board-Level Shields
These are the most common types of RF shields, and are commonly just referred to as an “RF shield”. They are through-hole or surface-mound metal casings which are soldered onto a PCB, and prevent RF either getting into or getting out of the components inside the shield.