An interactive applet and associated web page defining a circle. The applet shows a circle where the user can drag the center and a point on the circle. The radius line supports the definition that all points on the circle are a fixed distance from the center. The web page has the definitions of all the circle-related objects, such as diameter, chord, etc., with links for each.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.