1. Wire Gauge is a system for specifying the characteristics of wire.
See AMERICAN WIRE GAUGE and BIRMINGHAM WIRE GAUGE.
2. It is a wire number governed by diameter (e.g., 18-gauge wire for #18 wire).
3. It is a tool or instrument for measuring wire diameter or for determining wire number.
See also, Wiring, Wire Recorder, Wirewound Resistor, Wire Stripper