1. The perimeter or line describing a circle: Mrs. Lori taught her students how to calculate the circumferences of round objects.
2. The distance around the widest part of a boundary area or the periphery enclosing a circular space: Susan and Sally, who were hikers, walked the circumference of the lake and found that it took them two hours to complete their journey.

When Tim and his family were in Southern California during their vacation, they sailed around the entire circumference