The duplicate option allows you to copy the segment so that it can be refined without adjusting the originally saved segment. To duplicate, click Audience > Segments click the gear icon to the left of the segment that you would like to duplicate. Click the duplicate option in the drop-down menu once you click on the gear icon. The picture below indicates where this menu is located.
The duplicated segment will then open up on your screen. Further refine your data set by selecting different segment criteria. You can also rename your segment in the top left-hand corner where it says the segment name. Click save to save your new duplicated segment when you are finished.