Definition:Horizontal

Horizontal Line
Hence the adjective horizontally, meaning in a horizontal line.

Also presented as
The term the horizontal is frequently seen, particularly in the context of specifying the spatial orientation of a given (straight) line: the angle it makes to the horizontal.

In the context of the presentation of mathematical graphics on, for example, a piece of paper arranged horizontally, the horizontal is that direction to the left and right of the reader. Thus such a direction would be actually horizontal if that paper were held in a vertical plane oriented for normal reading.

It is of course noted that it is difficult at this level to define vertical and horizontal without the definitions at some point becoming circular. An appeal to an intuitive understanding is therefore necessary to a certain extent.

Also see

 * Definition:Vertical