What is Annus Deliberandi?

Legal Definition
In Scotch law. A year of deliberating; a year to deliberate. The year allowed by law to the heir to deliberate whether he will enter and represent his ancestor. It commences on the death of the ancestor, uniess in the case of a posthumous heir, when the year runs from his birth. Bell.
-- Black's Law Dictionary
Legal Definition
The year which the Scotch law gives the heir to determine whether he will take an inheritance.
-- Ballentine's Law Dictionary