An aluminum spool holding 100 feet of film with solid, opaque sides, painted black, which will protect the film from becoming completely exposed when loading a camera in daylight. The name daylight spool comes from the fact that the film may be loaded without total darkness. There are also 400 foot daylight spools, but these are very rarely used as they do not always work very well in a magazine.
Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/
reprinted with permission