noun

Imaginary Line: A straight line about which a body or geometric object rotates or may be conceived to rotate. For example, the Earth's rotation axis.

Reference Line: A fixed reference line for the measurement of coordinates. In a graph, the x-axis and y-axis are examples.

Example

1. The Earth's axis is tilted at an angle of 23.5 degrees, which causes the seasons.
2. The axis of the wheel is made of strong metal to withstand the weight of the car.
3. The mathematician plotted the data points on a graph with the x-axis representing time and the y-axis representing temperature.