1. A therapy or device designed to preserve someone's life when an essential bodily system is not doing so.  Life support may, for example, involve enteric feeding (by a tube), total parenteral nutrition , mechanical ventilation , a pacemaker , defibrillator , heart/lung machine, or dialysis . 2. Something that sustains life, as in "The earth is the ultimate life support system." 3. A product, program or company being propped up, as in "Medicare is on life support.