Perseus (Greek: Περσεύς; c. 150 BC) was an ancient Greek geometer, who invented the concept of spiric sections, in analogy to the conic sections studied by Apollonius of Perga.
Few details of Perseus' life are known, as he is mentioned only by Proclus and Geminus; none of his own works have survived.
Consequently, spiric sections are fourth-order (quartic) plane curves, whereas the conic sections are second-order (quadratic) plane curves.
The most famous spiric section is the Cassini oval, which is the locus of points having a constant product of distances to two foci.
For comparison, an ellipse has a constant sum of focal distances, a hyperbola has a constant difference of focal distances, and a circle has a constant ratio of focal distances.