What is a keeper in the theme of magnets?

A keeper is a steel bar or disc placed between and attached to opposite poles of a magnet to allow all magnetism to flow from one pole to the other. The held magnet appears completely non-magnetic until the keeper is removed. Holders were required for old Alnico magnets to preserve the magnetism of these low coercivity magnets. This is useful when transporting magnets in the air and containing stray magnetism. Neodymium, samarium cobalt and ferrite magnets do not need to be kept to protect their magnetism, but they are sometimes kept to make them safer to handle.