Folium (, "leaf"), plural folia, may refer to
a leaf of a book: see recto and verso Folium of Descartes, an algebraic curve Folium (spider), a marking on the abdomen of a spider
Brain anatomy Folium (brain) Folium vermis
Botany Turnsole or folium, a dyestuff Folium Phyllostachydis, processed leaves of bamboo Hydrangeae Dulcis Folium, processed leaves of hydrangea