A quad is short for quadrangle, a four-sided area or courtyard, especially at a college or university. Picture the open grassy or paved space surrounded by campus buildings where students gather between classes, toss frisbees, or study on sunny days. At many schools, the quad serves as the heart of campus life.

A quadrilateral is any four-sided shape in geometry. Quadruplets are four babies born at the same time. A quadruped is an animal that walks on four legs, like a horse or dog.

In informal speech, quad can mean other four-related things too. Some people use it as shorthand for the quadriceps, the group of four muscles on the front of your thigh. Athletes might say their quads are sore after running hills.