A copyright actually is a bundle of separate exclusive subrights, including the exclusive right to:
reproduce the work
display or perform the work
distribute the work, and
prepare adaptations of the work (derivative works).
When a copyright owner wishes to commercially exploit the work covered by the copyright, the owner typically transfers one or more of these rights to the publisher or other entity who will be responsible for getting the work to market. It is also common for the copyright owner to place some limitations on the exclusive rights being transferred. For example, the owner may limit the transfer to a specific period of time, allow the right to be exercised only in a specific part of the country or world, or require that the right be exercised only on certain computer platforms (those with UNIX operating systems, for example).
When all copyright rights are transferred unconditionally, it is generally termed an “assignment.” When only some of the rights associated with the copyright are transferred, it is known as a “license.” An exclusive license exists when the right being licensed can only be exercised by the licensee, and no one else. If the license allows others to exercise the same rights being transferred in the license, the license is said to be non-exclusive.
The U.S. Copyright Office allows buyers of exclusive and non-exclusive copyright rights to record the transfers in the U.S. Copyright Office. This helps to protect the buyers in case the original copyright owner later decides to transfer the same rights to another party.
Related terms: assignment of copyright; compulsory license; exclusive license, defined; grant of rights; licensing of copyrights; non-exclusive license; overlapping transfers of copyright; recordation of copyright transfers; revocation of license; shrink-wrap license; site license; termination of transfers; transfers of copyright ownership, generally.