The UCS dialog box allows you to create and manipulate User Coordinate Systems. The Current UCS drop down list shows the current coordinate system. Its coordinates in the World Coordinate System are displayed in the Parameters in World Coordinate Space box. By selecting a new UCS in the Current UCS drop down list, you change the active UCS. See How to change User Coordinate systems for more information.
The New button allows you to create a new UCS. See How to create a User Coordinate System for more information.
The translate, rotate, align, rename and reset buttons allow you to modify the current UCS. See How to modify a User Coordinate System for additional information.
To delete the current UCS, select the UCS name in the Current UCS drop down list and click the Delete button.
See User coordinate systems for more information on UCSs or How do setups relate to UCSs?.