Renewable energy refers to energy derived from naturally replenishing sources that are not depleted when used. These sources include solar, wind, hydroelectric, geothermal, and biomass energy. Unlike fossil fuels, which are finite and contribute to environmental pollution, renewable energy sources are sustainable and produce lower greenhouse gas emissions. Renewable energy technologies harness these natural resources to generate electricity, heat, or mechanical power, offering a cleaner and more sustainable alternative to traditional energy sources.