Question

what is vertical and horizontal​

Answer 1

In astronomy, geography, and related sciences and contexts, a direction or plane passing by a given point is said to be vertical if it contains the local gravity direction at that point. Conversely, a direction or plane is said to be horizontal if it is perpendicular to the vertical direction.

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Answer 2

A vertical line is any line parallel to the vertical direction. A horizontal line is any line normal to a vertical line.