Opening A Rule

The act of restoring or recalling a rule which has been made absolute to its conditional state, as a rule nisi,_ so as to readmit of cause being shown against the rule. Thus, when a rule to show cause has been made absolute under a mistaken impression that no counsel had been instructed to show cause against it, it is usual for the party at whose instance the rule was obtained to consent to have the rule opened, by which all the proceedings subsequent to the day when cause ought to have been shown against it are in effect nullified, and the Tule is then argued in the ordinary way.

Brown.