A CCP link is a "Cut, Copy & Paste link." It is created when you Copy something from one CATPart file (such as a Plane), and use Paste Special + As Result With Link to copy it into a second CATPart file. The CCP link provides a parent/child relationship between the two parts, so that if the parent plane is modified (re-positioned), the child plane will follow when the second CATPart file is Updated.
I strongly recommend using Publications with this type of link.