A system is self-sustaining (or self-sufficient) if it can maintain itself by independent effort. The system self-sustainability is the degree at which the system can sustain itself without external support the fraction of time in which the system is self-sustaining. Self-sustainability is considered one of the "ilities" and is closely related to sustainability and availability. In the Economics literature, a system that has the quality of being self-sustaining is also referred to as an autarky.