What is Vis Impressa?

Legal Definition
Immediate force; original force. This phrase is applied to cases of trespass when a question arises whether an injury has been caused by a direct force, or one which is indirect. When the original force, or vis impressa, had ceased to act before the injury commenced, then there is no force, the effect is mediate, and the proper remedy is trespass on the case.

2. When the injury is the immediate consequence of the force or vis proxima, trespass vi et armis lies. 3 Bouv. Inst. n. 3483; 4 Bouv. Inst. n. 3583.
-- Bouviers Law Dictionary
Legal Definition
The original act of force out of which an injury arises, as distinguished from "vis proxima," the proximate force, or immediate cause of the injury. 2 Greenl. Ev. ยง 224.
-- Black's Law Dictionary
Legal Definition
Immediate or proximate force.
-- Ballentine's Law Dictionary