The term "category romance" derives from the fact that the books are published in clearly delineated categories, with a certain number of books being published in each category every month. Their alternative name, series romances, came from the sequential numbers sometimes printed on the books' spines. Category romances are short (usually no more than 250 pages), and have a low purchase price compared to other fiction books. These series or category books are also often considered to be one of the many romance genres.