'Tangent plane' definitions:

Definition of 'tangent plane'

(from WordNet)
noun
The plane that contains all the lines tangent to a specific point on a surface

Definition of 'Tangent plane'

From: GCIDE
  • Tangent \Tan"gent\, a. [L. tangens, -entis, p. pr.] Touching; touching at a single point; specifically (Geom.) meeting a curve or surface at a point and having at that point the same direction as the curve or surface; -- said of a straight line, curve, or surface; as, a line tangent to a curve; a curve tangent to a surface; tangent surfaces. [1913 Webster]
  • Tangent plane (Geom.), a plane which touches a surface in a point or line.
  • Tangent scale (Gun.), a kind of breech sight for a cannon.
  • Tangent screw (Mach.), an endless screw; a worm. [1913 Webster] [1913 Webster]