Shield is a broad piece of armor, varying in size and shape, carried apart from the body, usually on the left arm, to ward off blows or missiles.
In modern usage, shield can also refer to:
1. A protective device or structure
2. Something that resembles a shield in form or function
3. A person or thing that provides protection
4. In heraldry, the escutcheon or field on which are placed the bearings in coats of arms
5. In geology, a large stable area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks