A vertical axis is an imaginary line that runs up and down, perpendicular to the horizontal plane. It is commonly used in various fields, such as mathematics, physics, and engineering, to represent data or movement. For example, in a graph, the vertical axis often displays values or measurements, allowing for easy comparison with the horizontal axis, which typically represents categories or time. In the context of machinery, a vertical axis can refer to the orientation of rotating parts, such as in a vertical axis wind turbine. This design allows the turbine blades to rotate around a vertical line, capturing wind energy efficiently from any direction.