A tripod is a three-legged stand that holds a piece of equipment steady. Most often it is for a camera: you screw the camera onto the top, spread the three legs, and the picture comes out sharp even in low light or during a long exposure. But the word covers any three-legged support — for a telescope, a microphone, a surveyor's instrument, a stage light, even an old cooking pot over a fire. Why three legs and not four? Three points always touch the ground at once, so a tripod does not wobble on uneven ground the way a four-legged stand does; this is worth telling a student, because it explains why the shape has survived for thousands of years. In everyday speech, the word is so ordinary among photographers that it works as a verb-ish noun: 'I'll shoot it on a tripod.' The little one you stand on a table is a tabletop tripod, and the flexible-legged kind is usually called by its brand name.