Transferring one's rights under a contract to another while retaining secondary liability is called?

The term that describes transferring one's rights under a contract to another while retaining secondary liability is "assignment." In an assignment, the assignor transfers their rights to a third party (the assignee), but remains liable for the performance of obligations under the original contract if the assignee fails to fulfill them. This means that while the assignee has the right to enforce those rights, the original party still holds responsibility towards the other party in the contract.

This concept is distinct from delegation, which involves transferring duties or obligations to another party, whereby the delegator may remain liable unless a novation occurs. In novation, both parties must agree to substitute a new party for one of the original parties, which releases the original party from liability. Modification refers to changes made to the terms of a contract, rather than transferring rights or responsibilities. Thus, "assignment" is the correct answer as it specifically addresses the transfer of rights while maintaining secondary liability.