A capacitor is a small electrical part that collects electric charge, holds it for a short time, and then lets it go. Phones, radios, computers, and camera flashes are full of them. Think of it as a tiny bucket for electricity: it fills, it holds, it empties, very fast. You meet the word in science class and in repair manuals, not at the dinner table. Most capacitors are little discs or cylinders sitting on a circuit board, not a big machine in a room.

Older books, and some older engineers, still call this a condenser. That older name caused trouble, because condenser also means the part of a steam engine that turns steam back into water. Alessandro Volta coined condenser for the electrical part in 1782. In 1926 a British list of electrical terms recommended capacitor instead, so the two machines would not share a name. Nobody is sure who first said capacitor. In Taiwan class talk, students often shorten the Chinese to 電容; the full name is the part itself.