Latin: of marriage.
This used to be distinguished from a divorce a mensa et thoro.
In a 1923 Dictionary of English Law by W. J. Byrne (London: Sweet & Maxwell) page 315, this distinction is offered:
"(A divorce) was of two kinds - a divorce a mensa et thoro (from bed and board), granted in cases where the husband or wife had been guilty of such conduct as to make conjugal intercourse impossible (as in the case of adultery, cruelty etc.); and a divorce a vinculo matrimonii (from the bond of marriage), granted where the marriage was voidable or void ab initio (as in the case of the parties being within the prohibited degrees (of relation), or one of them having been previously married, or being impotent when married).
The term - when used - now refers to a final and permanent divorce.