the property of being sustainable
"The sustainability of our renewable energy projects ensures they can operate indefinitely without depleting resources."
The ability to sustain something.
"The forest's sustainability depends on harvesting trees at a rate that allows new growth to replace those cut down."
In plain English: Sustainability is using resources carefully so they last forever and don't run out for future generations.
"The city council approved new recycling programs to improve sustainability in our community."
The word sustainability combines the root sustain, meaning to hold up or endure, with the suffix -ability to indicate a quality of being able to be sustained. It entered English as a modern formation describing the capacity to maintain something over time without depletion.