What is Ex Turpi Contractu Actio Non Oritur?

Legal Definition
From an immoral or iniquitous contract an action does not arise. A contract founded upon an illegal or immoral consideration cannot be enforced by action. 2 Kent, Comm. 466; Dig. 2, 14, 27, 4.
-- Black's Law Dictionary
Legal Definition
From an evil contract no action arises. See 44 Minn. 318, 20 Am. St. Rep. 580, 9 L. R. A. 506, 46 N. W. 558.
-- Ballentine's Law Dictionary