What is Foreign Plea?

Legal Definition
One which, if true, carries the cause out of the court where it is brought, by showing that the matter alleged is not within its jurisdiction. 2 Lill. Pr. Reg. 374; Carth. 402; Lill. Ent. 475. It must be on oath and before imparlance. Bac. Ab. Abatement, R.
-- Bouviers Law Dictionary
Legal Definition
A plea objecting to the jurisdiction of a judge, on the ground that he had not cognizance of the subject-matter of the suit. Cowell.
-- Black's Law Dictionary