The clipboard is a holder for various kinds of objects (regions, control events, plugins) that is used during cut-and-paste operations.

Cut

A cut operation removes selected objects and places them in the clipboard. The existing contents of the clipboard are overwriten.
The default key binding is x.

Copy

A copy of the selected objects are placed in clipboard. There is no effect on the selected objects themselves. The existing contents of the clipboard are overwritten.
The default key binding is c.

Paste

The current contents of the clipboard are pasted (inserted) into the session, using the current edit point as the destination. The contents of the clipboard remain unchanged — you can paste the same item multiple times.
The default key binding is v.