Folium \Fo"li*um\, n.; pl. E. Foliums, L. Folia. [L., a leaf.]

1. A leaf, esp. a thin leaf or plate.

2. (Geom.) A curve of the third order, consisting of two infinite branches, which have a common asymptote. The curve has a double point, and a leaf-shaped loop; whence the name. Its equation is x^3 + y^3 = axy.

Source: Webster's Revised Unabridged Dictionary (1913)