Calculus: 1. A stone within the body, such as a stone in the urinary tract. 2. The calcium salt deposits on the teeth. 3. A field of mathematics. These different meanings of "calculus" all go bach to the origin of the word. In Latin, a calculus is "a pebble." Pebbles were once used for counting, from which came the mathematical field of calculus. A urinary calculus is a literally pebble in the urinary system. And the calculus on the teeth is, like a urinary stone, an abnormal concretion of mineral salts within the body.