The genizah, Hebrew for "hiding place," is a depository for sacred Hebrew books that are no longer usable. Since they cannot be discarded in a normal manner because they contain God's name, these documents, often called shemotor ("names"), are put in a genizah.
Genizot are usually found in the attic or basement of a synagogue, but can also be in walls or buried underground, as we are doing. Non-religious documents can be put there, as well.
A Genizah traditionally served a dual purpose. It served as a repository for books no longer used and it also hid books that were banned by the realm so they could be retrieved for sacred purposes.