From The Stargate Omnipedia
Ancient containment vessel
Device of Ancient
construction which encapsulates its contents in a layer of subspace. The Ancients were using this technology during the height of their war with the Wraith
. It was used to enhance their scientific knowledge of ascension.
Because the substance contained is stored in subspace, an object of virtually any manageable size can be encased within.
Hide and Seek - Jinto inadvertently activates an Ancient containment vessel's release program, allowing a shadow creature captured within to run free.