An operator is someone who runs or controls a machine, system, or piece of equipment. A crane operator sits high in the cabin of a construction crane, carefully moving heavy steel beams into place. A radio operator sends and receives messages over radio waves. A telephone operator (in the days before automated phone systems) connected people's calls by plugging wires into a switchboard.

The job requires skill and attention because operators make important decisions about how their machines work. A skilled backhoe operator can dig a precise trench without damaging underground pipes. A nuclear power plant operator monitors complex systems to keep the reactor running safely.

In math, an operator is a symbol that tells you what to do with numbers. The plus sign (+) is an operator that means “add these numbers together.” The multiplication sign (×) is an operator that means “multiply.” When you see 5 + 3, the operator tells you to combine those numbers.

People sometimes use operator informally to describe someone who's clever at getting what they want, sometimes in a slightly sneaky way. If someone calls your friend a “smooth operator,” they mean he's good at talking his way into or out of situations.