Royalty Free (RF)
This is a licensing term used in the creative industry of stock photography that enables a stock photo buyer to use a purchased photo as many times as the stock agency license outlines in their terms and conditions without having to pay a royalty to the photographer. In many creative arts industries, royalties are paid to the creator (musicians, authors) when a creative piece is sold over and over again. If you are familiar with royalties in other creative or arts based industries this makes sense. Stock photo agencies did not want to have to track how many times a photos was used by a buyer hence the term royalty free.