According to Wikipedia

A circular economy is an economic system aimed at minimising waste and making the most of resources. This regenerative approach is in contrast to the traditional linear economy, which has a ‘take, make, dispose’ model of production. In a circular system resource input and waste, emission, and energy leakage are minimized by slowing, closing, and narrowing energy and material loops; this can be achieved through long-lasting design, maintenance, repair, reuse, remanufacturing, refurbishing, recycling, and upcycling.

The Ellen MacArthur Foundation says

Looking beyond the current take-make-waste extractive industrial model, a circular economy aims to redefine growth, focusing on positive society-wide benefits. It entails gradually decoupling economic activity from the consumption of finite resources, and designing waste out of the system. Underpinned by a transition to renewable energy sources, the circular model builds economic, natural, and social capital. It is based on three principles:
– Design out waste and pollution
– Keep products and materials in use
– Regenerate natural systems