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, Dürer folium, and the rose curves.
When used without qualification, the term "folium" commonly refers to Kepler's folium (Lawrence 1972, pp. 152-153; MacTutor).
The rose curve with parameter 
is folium with 
petals (for 
odd) or 
petals (for 
even).
