What is Ad Factum Praestandum?

Legal Definition
In Scotch law. A name descriptive of a class of obligations marked by unusual severity. A debtor who is under an obligation of this kind cannot claim the benefit of the act of grace, the privilege of sanctuary or the cessio bonorum. Ersk. Inst. llb. 3, tit. 3, § 62.
-- Black's Law Dictionary
Legal Definition
A Scotch law obligation of a very binding nature.
-- Ballentine's Law Dictionary