Round things are either shaped like circles or have curves, like a baby's round belly or a round basketball.
A cookie is usually round, and so is Santa Claus. When you use round as a verb, it means to form something into a circular or spherical shape: "Round the dough and then press it into the pan." In math, round means to go up or down to the nearest whole number: "Round the bill up before you figure out how much to tip your server." The Latin root, rotundus, means "like a wheel."