This is taken from our procedural manual for the Collections Department:

Museum Use Collections:

In addition to the permanent collection, the museum maintains a museum use
collection. These are items that are used for education programs, traveling
artifact kits, and other educational purposes.  They are not given the same
care and attention as permanent collection artifacts because they are
designated to be handled, used, and eventually used up or worn out and
disposed of.  Upon the  recommendation of the curator or archivist, incoming
material may be designated for the museum use collections. The curator or
archivist will inform the donor of their intent so that they understand the
times will not become part of the permanent collection.

Procedures for accessioning museum use items are virtually the same as those
used for permanent collection items except that they are assigned an
accession number that is followed by the letters "MU."  Museum use items are
not photographed, and are turned over to the Museum's public programs
coordinator.