What is Contra Formam Feoffamenti?

Legal Definition
In English law, contra formam feoffamenti was a writ for a tenant who was infeoffed by the lord's charter to make certain suit and service to his court, and was afterwards distrained for more than was contained therein.
-- Wikipedia
Legal Definition
A writ whereby a tenant could resist the demanded performance of more services than the charter of his ancestor required.
-- Ballentine's Law Dictionary