A roadway intersection where the roads don't directly cross (like at a stoplight) but enter/exit on a circular road. When well designed it is very superior to a normal intersection, but prone to confuse people who learned to drive in a place without them. Poorly designed or outdated they are a recipe for disaster.
If you live in New Jersey, but don't know what a traffic circle is, you're living an unbelievably sheltered life.
When correctly designed, you should always yield when entering the circle, but never when in the circle.