Nappe \Nappe\, n. [F. nappe cloth, sheet. See {Napery}.] (Geom.)
Sheet; surface; all that portion of a surface that is
continuous in such a way that it is possible to pass from any
one point of the portion to any other point of the portion
without leaving the surface. Thus, some hyperboloids have one
nappe, and some have two.
[1913 Webster]