What is an axis?
http://www.google.com/search?q=define%3Aaxis&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
It is a fixed reference line from which position is measured or plotted.
An axis is an imaginary line around which an object rotates or something is measured. In the context of geometry or coordinate systems, an axis is a reference line used to define the position or movement of points or objects.
To understand what an axis is, imagine a simple coordinate system like a Cartesian coordinate system. This system consists of two axes: the x-axis (horizontal) and the y-axis (vertical). The intersection of these axes at a point called the origin marks the (0,0) position.
To define a point on this coordinate system, you need to specify its distance along the x-axis (horizontal) and the y-axis (vertical) from the origin. The x-axis represents the horizontal position and the y-axis represents the vertical position.
Similarly, in three-dimensional space, there is an additional axis known as the z-axis that represents the depth or height. Together, these three axes (x, y, and z) form a three-dimensional coordinate system.
In summary, an axis is an imaginary line used as a reference to describe the position, rotation, or measurements of objects in mathematical or geometric systems.