I've found that the "rights-managed" and "rights managed" are used equally in the stock photography world, but both mean the same thing-rights are licensed with respect to a specific use by the licensee, often on an exclusive basis in exchange for a license fee but any other use requires a separate fee to be paid. Contrast with "royalty-free" or "royalty free" (again, not consistent) licenses.
Sorry for the law lesson, thought there might be enough people interested in photography on the site not to mind.
T