Renewable describes resources that naturally replace themselves over time, so we can keep using them without running out. Sunlight, wind, and water flowing in rivers are renewable because they keep coming back. Trees are renewable because we can plant new ones to replace those we cut down.

The opposite of renewable is nonrenewable: resources like coal, oil, and natural gas took millions of years to form underground, and once we use them up, they're gone. We call renewable resources that generate power, like sunshine or wind, renewable energy because they can keep producing electricity without being depleted.

The concept matters because Earth has limited nonrenewable resources. When engineers design solar panels to capture sunlight or build wind turbines to harness wind, they're creating ways to use renewable energy. A forest managed carefully can be a renewable resource: if you plant two trees for every one you harvest, the forest renews itself.

Think of it like your allowance: if you spend everything and get no more, that's nonrenewable. But if you earn new allowance each week, that's renewable too.