An Ellipse or Hyperbola.
References
Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 146-150, 1967. Ogilvy, C. S. Excursions in Geometry. New York: Dover, p. 77, 1990.
Ogilvy, C. S. Excursions in Geometry. New York: Dover, p. 77, 1990.