A maser is a machine that makes a very strong, tight beam of microwave energy. The name is letters said as a word: Microwave Amplification by Stimulated Emission of Radiation. People usually meet laser first; a maser is the same kind of idea, but it uses microwaves, not light you can see. Dictionary lines sometimes say it makes a “powerful electric force,” though actually that is a little loose — it is not a shock from a wire. It is a controlled wave of energy. You meet the word in science class or labs, almost never in daily talk.

微波激射器。有人比照「雷射」叫「脈射」，但課堂上較完整的說法是微波激射器。