Axis

Keywords: XYZ

The axis refer to the different cardinal directions that define your world coordinate system. On a 2d screen you can move in two axis or directions. X (Left and Right) and Y (Up and Down). In 3d you add one more direction: Z. This is often seen as in and out of the screen. However, some engines swap these around so Z is up instead. To get a better understanding of this, you can read more about three diminsional coordinate systems here:

https://en.wikipedia.org/wiki/Three-dimensional_space