Vault terminology?

[Orrus]

Whats the difference between a lesser vault and a greater vault, just size?

In this picture, there is a lesser vault in the top right, and a what in the bottom left? Are there random vaults with non indestructable walls?

[Nick]

The dungeon generation algorithm treats them differently. If you look at lib/edit/vault.txt, it explains a lot.

[Orrus]

What are the random vault like rooms? The one in the screenshot above is not in v_info.txt. Its full of loot and uniques like a vault, but theres no doors or "rooms"? How does it create those? Is it like a miniature "arena" level?