Sustainable means able to continue over a long period without running out of resources or causing permanent damage. When something is sustainable, it can keep going because it doesn't use up more than can be naturally replaced or renewed.

A sustainable fishing practice catches only some of the fish in the ocean, leaving enough behind to reproduce and maintain healthy populations for the future. A sustainable forest is one where loggers cut down some trees but plant new ones, so the forest keeps thriving decade after decade. A family farm might use sustainable methods by rotating crops, which means planting different things each season so the soil stays healthy and fertile instead of wearing out.

The opposite of sustainable is something that depletes resources faster than they can recover. If a town pumps all the water from its underground aquifer without letting it refill, that's not sustainable. Eventually, the wells run dry.

When people talk about sustainability, they're asking an important question: can we keep doing this without ruining things for ourselves or future generations? A sustainable practice works for years and decades to come, continuing indefinitely without depleting what it depends on. It's the difference between eating all your Halloween candy in one night and making it last by having just a piece or two each day.