i am doing research on selling photos. i often come across the term 'royalty free' images or license. i am trying to grasp its exact meaning.

as i understand if you sell a royalty free image the buyer may utilize the image in whatever way they wish ie. advertisments, calenders, broachers ect...but you as the seller still hold the RIGHTS to the photograph. that meaning you may still SELL the pic to another buyer. am
i right? correct me if i am wrong.