A system of ethics that evaluates acts in light of their situational context rather than by the application of moral absolutes.
Imagine you are invited to dinner at the house of a friend. You arrive, exchange polite conversation, enjoy a few appetizers and sit down at the table. Midway through the main course you suddenly begin shouting at the other guests, overturning the chairs, grab the host out of his chair and begin physically assaulting him.
That would be considered highly inappropriate behavior - unless, of course, you had just observed him choking, you took charge of the situation, instructing one guest to call for help, another to wait outside and flag down the ambulance while you cleared obstructions out of the way and administered the life-saving Heimlich maneuver.