closed curve
curve whose starting point coincides with its ending point; continuous image of a circle
closed timelike curve
worldline (timelike curve) in a Lorentzian manifold that is closed (returns to its starting point)
cartesian oval
the set of points that have the same linear combination of distances from two fixed points
oval
shape
loop
in mathematical topology, a path whose initial point is equal to its terminal point
flight to nowhere
type of commercial flight
n-ellipse
generalization of the ellipse allowing more than two foci
simple closed curve
closed curve with no intersection