At right angles to, going directly away from.

For a curve imagine a line just touching and matching the slope there (called a "tangent") and draw a line at right angles to it.

Likewise for a curved surface imagine a plane sitting on the surface, and draw a Normal to that plane.

For a curve imagine a line just touching and matching the slope there (called a "tangent") and draw a line at right angles to it.

Likewise for a curved surface imagine a plane sitting on the surface, and draw a Normal to that plane.

See: Tangent (line)

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