An ossuary is a chest, building or other type of site (like a catacomb) that serves as a final resting place for human skeletal remains.
In some places, exhumation after traditional burial (usually quite awhile after – such as 20 years – to give the remains time to decompose to a skeletal state) is performed to condense the remains into an ossuary, generally done to preserve as much room as possible in a burial plot or crypt. Re-interring remains in the much-smaller ossuary assures more room for others to be buried in a site.