In 3D Modeling and in 3D Printing itself, axes (plural of axis) are used a lot to define directions and parts on a 3D Printer. An axis is an imaginary line used for directional purposes and to help you figure out which way is ‘up.’ There are 3 axes, X, Y, and Z. There is a very simple way to think of it, and it revolves around the introduction to axes in the early years of high school math. In Algebra, there are two axes, the X and the Y. The Y axis always points towards the top and bottom of the paper on a grid, the X points to the left and the right. The Z axis, if it were there, would stick up directly out of the origin, and come up out of the paper.

This concept also applies in 3D Printing, when designing. The part of the object you want to face up, you design to have it placed upwards on the Z axis, allowing you to not have to re-orient the object for printing. So, in common terms, the Z axis is up, and the X and Y axes are going the other two directions. Also note that the lines extend forever infinitely, so there is a way to have the Z axis be below the origin.