The "Plane" class represents a theoretical plane in 3d space, used for mathematical and geometric calculations - which is different from the Plane primitive found in the editor, which is a bit like a prefab GameObject with a Mesh Filter, Mesh Collider and Mesh renderer components attached.
There's also a "CreatePlane" script on the wiki, if you want to be able to specify the number of faces used in your plane.
The Plane class does not represent a graphical objects - it's just a mathematical plane used for calculations -- which side of the plane an object is, where a ray intersects the plane, etc.
You can create a graphical plane mesh using the GameObject->Create New->Plane menu command.
answered Dec 02 '09 at 11:28 AM
jonas echterhoff ♦♦