As you create or move objects, you can use Ortho mode to restrict the cursor to the horizontal or vertical axis found along the UCS icon. It is recommended to leave Ortho mode turned on while in the drawing environment. This will help ensure that an object is moved in the desired direction. Using the direct distance entry method with Ortho mode turned on is a quick method to move objects. While in a 3D view, the cursor will not only be restricted along the X and Y-axis but also allow restricted movement along the Z-axis.
With Ortho Mode turned on, the cursor is restricted along the axis.
With Ortho Mode turned off, the cursor is unrestricted.
Ortho Mode can be activated or deactivated with the F8 command key, or by using the button near the bottom of the screen.