In mathematics, an axis is a designator for a Cartesian-coordinate [笛卡尔坐标系] dimension.

Rotation around a fixed axis is typically taught in introductory physics courses after students have mastered linear motion; the full generality of rotational motion is not usually taught in introductory physics classes.

An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. For an optical fiber, the optical axis is along the center of the fiber core, and is also known as the fiber axis.

In anatomy, the axis is the second cervical vertebra of the spine, immediately posterior to the atlas, upon which the head rests.

在解剖学上，中轴是脊椎的第二个颈椎，位于寰椎的正后方，头部靠在其上。

The Axis powers, also known as the Rome–Berlin–Tokyo Axis, were the nations that fought in World War II against the Allied Powers. The Axis agreed on their opposition to the Allies, but did not completely coordinate their activity.