circumference | The distance around a circle, calculated by the formula C = d. |
diameter | The length across a circle, passing through the center of the circle. A diameter is equal to the length of two radii. |
pi | The ratio of a circle’s circumference to its diameter. Pi is denoted by the Greek letter . It is often approximated as 3.14 or. |
radius | The distance from the center of a circle to any point on the circle. |