What is a metal or concrete enclosure designed to protect the casket called?

A metal or concrete enclosure designed to protect the casket is referred to as a vault. The primary purpose of a burial vault is to provide structural integrity and protection for the casket from the weight of the surrounding earth, as well as to prevent the grave from sinking over time.

Burial vaults can also help to protect the casket from environmental elements, such as water and soil, which can lead to premature deterioration. This ensures that the casket and its contents are preserved for a longer period.

In contrast, a niche is a space designed to hold cremated remains, typically found in a columbarium, which itself is a structure providing multiple niches. An urn is a container used specifically for holding cremated remains, and does not denote a specific protective structure. While each of these terms relates to mortuary practices, the term that directly describes a protective enclosure for a casket is vault.