I posted this on another thread. It is called "First Sale Doctrine""
The doctrine allows the purchaser to transfer (i.e., sell, lend or give away) a particular lawfully made copy of the copyrighted work without permission once it has been obtained. This means that the copyright holder's rights to control the change of ownership of a particular copy ends once ownership of that copy has passed to someone else, as long as the copy itself is not an infringing copy. This doctrine is also referred to as the "right of first sale," "first sale rule," or "exhaustion rule."