For Trademarks: An assignments is a transfer of ownership of a trademark application or trademark registration from one entity to another.
For Patents: An assignment involves the sale and transfer of ownership of a patent by the assignor to the assignee.
The assignee is the entity that is the recipient of a transfer of a patent application, patent, trademark application or trademark registration from its owner on record (assignor).
The assignor is the owner on record of a patent application, patent, trademark application or trademark registration who is transferring (assigning) ownership to another entity (assignee).
You can assign the ownership of a patent application or patent. For all U.S. patented record all assignments with the USPTO Assignment Services Division to keep clear the title to pending patent applications and patents.
Sometimes an assignment is mandatory, such as where employee inventions are assigned by an employee to the employer because of the contract that the employee has signed.
In contrast to patent licensing, an assignment is irrevocable. This transfer of ownership is permanent and irrevocable.