👉 In mathematics, a "z-axis" is a coordinate axis in a two-dimensional plane. It represents the horizontal direction on a Cartesian coordinate system and is perpendicular to the vertical direction. The z-axis is often used for representing spatial dimensions or for plotting coordinates.
For example, if we have a 2D plot with x and y axes, the z-axis could be represented by the line that runs through the origin (0,0) and points up, as shown in this image:
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zaxes