A catacomb is a type of underground grave found in Rome Italy. They usually had lots of tunnels and were sort of maze like. So a catacomb is technically a good place to bury someone as it a type of cemetery. But the Catholics also used it to hide from those persecuting them and to also hold secret services of the holy sacrament of the Eucharist (Mass).
Hope that helped! If you have any other questions or would like further explanation just let me know! :)
