What is A Mensa Et Thoro?

Legal Definition
From bed and board. A divorce a mensa et thoro, is rather a separation of the parties by act of law, than a dissolution of the marriage. It may be granted for the causes of extreme cruelty or desertion of the wife by the husband. 2 Eccl. Rep. 208. This kind of divorce does not affect the legitimacy of children, nor authorize a second marriage. V. A vinculo matrimonii; Cruelty Divorce.
-- Bouviers Law Dictionary
Legal Definition
"From table and bed". Divorce a mensa et thoro indicates legal separation without legal divorce.