Noun
groin vault (plural groin vaults)
(architecture) A vault resulting from the intersection of two barrel-vaults crossing in a right angle. Its thrusts are concentrated along the groins or arrises and eventually at the four corners
However, whereas in a groin vault, the vault itself is the structural member, in a ribbed vault, it is the ribs that are the structural members, and the spaces between them can be filled with lighter, non-structural material. Source: Internet
In ribbed vaults, not only are there ribs spanning the vaulted area transversely, but each vaulted bay has diagonal ribs, following the same course as the groins in a groin vault. Source: Internet