What is Borg?

Legal Definition
In Saxon law. A pledge, pledge giver or surety. The name given among the Saxons to the head of each family composing a tithing or decennary, each being the pledge for the good conduct of the others. Also the contract or engagement of suretyship; and the pledge giver
-- Black's Law Dictionary
Legal Definition
Same as Borgh.
-- Ballentine's Law Dictionary