Sacred treasures. It refers to treasures which are kept in the honden or homotsu-den (treasure-hall) of a shrine and regarded as the belongings of the kami. The treasures, which are likely to be kept securely wrapped and enclosed (cf. sanshu no shinki, the imperial regalia) and whose identity may even be uncertain, can be items such as works of art, sacred garments, weapons, musical instruments, bells and mirrors.
A Popular Dictionary of Shinto. Brian Bocking.