In a cemetery, what defines a vault, as opposed to a simple brick lined grave?

"A burial vault is a structural underground tomb. It is a stone or brick-lined underground space or 'burial' chamber for the interment of a dead body or bodies. They were originally and are still often vaulted and usually have stone slab entrances. They are often privately owned and used for specific family or other groups, but usually stand beneath a public religious building, such as a church, or in a churchyard or cemetery. A crypt may be used as a burial vault."
https://en.wikipedia.org/wiki/Burial_vault_(tomb)

In other words, a vault is a fully-constructed chamber, including roof, not just a brick-lined hole.

There are three kinds of burial vaults that vary in price, functionality and the material from which they are made. A grave box is the most basic burial vault. Made from concrete, grave boxes are unlined and have holes in the bottom to allow water to flow through freely. The grave box is the most cost effective. A bell vault is made of lightweight material like plastic. Constructed to be easily stacked, bell vaults are kept above ground and are moderately expensive. The top-of-the-line burial vault is the lined burial vault. Offering the greatest protection to the casket and surrounding ground, the lined burial vault is the most expensive.

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