“Mischief Rule” – This is used in statute interpretation. When an Act aims to cure a defect in the law, any ambiguity is to be resolved in such a way as to favour that aim.
A Mischief Rule interpretation would look at the common law that existed before the Act was created; the mischief that the common law created or did not remedy; the legislative remedy Parliament proposed; and the reason for that remedy.
See and contrast:
Hill v. R., 1975 CanLII 38 (SCC),  1 SCR 827
Regional Assessment Commissioner v. Ontario Steel Products, 1973 CanLII 52 (ON CA)