- a curve generated by the motion of a point on the circumference of a circle that rolls externally, without slipping, on a fixed circle. Equation: x = (a + b) cos(θ) − b cos[(a + b)θ/b] and y = (a + b) sin(θ) − b sin[(a + b)θ/b].
- the curve described by a point on the circumference of a circle as this circle rolls around the outside of another fixed circle, the two circles being coplanar
