资料来源 : Webster's Revised Unabridged Dictionary (1913)

Plane \Plane\, a. [L. planus: cf. F. plan. See {Plan}, a.]
   Without elevations or depressions; even; level; flat; lying
   in, or constituting, a plane; as, a plane surface.

   Note: In science, this word (instead of plain) is almost
         exclusively used to designate a flat or level surface.

   {Plane angle}, the angle included between two straight lines
      in a plane.

   {Plane chart}, {Plane curve}. See under {Chart} and {Curve}.
      

   {Plane figure}, a figure all points of which lie in the same
      plane. If bounded by straight lines it is a rectilinear
      plane figure, if by curved lines it is a curvilinear plane
      figure.

   {Plane geometry}, that part of geometry which treats of the
      relations and properties of plane figures.

   {Plane problem}, a problem which can be solved geometrically
      by the aid of the right line and circle only.

   {Plane sailing} (Naut.), the method of computing a ship's
      place and course on the supposition that the earth's
      surface is a plane.

   {Plane scale} (Naut.), a scale for the use of navigators, on
      which are graduated chords, sines, tangents, secants,
      rhumbs, geographical miles, etc.

   {Plane surveying}, surveying in which the curvature of the
      earth is disregarded; ordinary field and topographical
      surveying of tracts of moderate extent.

   {Plane table}, an instrument used for plotting the lines of a
      survey on paper in the field.

   {Plane trigonometry}, the branch of trigonometry in which its
      principles are applied to plane triangles.

资料来源 : WordNet®

plane angle
     n : an angle formed by two straight lines (in the same plane)