A circle is defined as a set of points in a plane that are all the same distance from a central point. This fixed distance is called the radius. Common examples of circles include the rims of buckets, drums, and clocks. Key terms related to circles include: - Center: The fixed point that defines the circle - Radius: The fixed distance from the center to any point on the circle - Diameter: A chord passing through the center that is the longest chord in the circle - Circumference: The distance around the outside of the circle - Chord: A line segment connecting any two points on the circle.