The camber link is the upper link that attaches the wheel's hub to the chassis. In most cars this is a tie-rod with ball cups at each end, but in some cars (usually 1/8th scale) it is an arm, similar to the lower arm.
Changing the length of the camber link adjusts the camber. Changing its mounting positions can affect roll center or camber gain, or both (see images below for details.)
Read our article on camber for details.