The term folium means "leaf" in Latin and refers and refers to a plane curve having "leaf-shaped" rounded lobes. There are a number of different
sorts of folia, including Kepler's folium, the
folium of Descartes, and Dürer
folium.
When used without qualification, the term "folium" commonly refers to Kepler's folium (Lawrence 1972, pp. 152-153;
MacTutor).
