what is the difference between a NURBS curve and a NURBS surface?

what is the the difference between adding a NURBS curve form the path
add>curve> NURBS curve
add>surface>NURBS curve?

can someone explain? thanks


add>>Curve>>Nurbs Curve is a one dimensional construct, that can be a path and can be beveled and tapered. You cannot extrude a curve>>nurbs curve perpendicularly to its own length to make a two dimensional surface (you can, however, give it an extrude parameter, which will make it appear as a surface, just as taper and bevel do.)

add>>Surface>>Nurbs Curve is a two dimensional construct (containing only a line when added) which cannot be used as a path, cannot be beveled or tapered, but can be extruded perpendicular to it’s own length into a nurbs surface.