A mirror is a smooth surface that reflects images. The word does not occur in the King James Version, but the idea is there. It is translated from the Hebrew or Greek as "glass," "glasses," or "looking glass." Modern translations use "mirror."
Mirrors in biblical times were made of polished metal such as copper, bronze, silver, gold, or electrum (a mix of gold and silver). People polished these metal surfaces until they were very smooth so they could see their reflection as clearly as possible.
Glass existed during biblical times, but it was usually not clear enough to see through (opaque). The exception was Roman glass, which was clearer. However, people did not use glass for mirrors until after the biblical period ended.
The Bible first mentions mirrors in the time of Moses. It relates to building the tabernacle in the Sinai wilderness after the exodus from Egypt (Exodus 38:8). When Alexander the Great spread Greek culture, mirrors became more common in the biblical world. Until that time, they were the possessions of either court ladies or prostitutes.
Archaeological digs in Palestine have found bronze mirrors as well as women's jewelry and clothes. Most of these date from the time after the exile to Babylon up through Roman times. The mirrors are usually circular in shape with handles of wood or ivory (if they have handles at all).