The hierarchy of 3d models is like this [top down for this example ]
 A vert or vertex one spot plotted in 3d space , you need 3 in order to form any primitive shape.
 3 verts connected by 3 edges makes one face , : aka a tri / 3 verts
 2 faces side by side sharing verts makes up one poly : aka a quad / 4 verts
 All faces or poly’s joined together makes up your mesh : aka an element / all verts
this should help