A trade name for a type of card file; as, a Rolodex(R) card file. Also used informally and improperly as a noun meaning Rolodex(R) card file.

A Rolodex is a rotating file device used to store business contact information (the name is a portmanteau of Rolling and Index) currently manufactured by Newell Rubbermaid. The Rolodex holds specially shaped index cards; the user writes the contact information for one person or company on each card. Many users avoid the effort of writing by taping the contact's business card directly to the Rolodex index card.

a wonderful substitute for actual knowledge

a must to be considered