Alternative energy refers to energy sources that are different from traditional fossil fuels like coal and oil. Some common examples include solar energy (from the sun), wind energy (from the wind), hydropower (from flowing water), geothermal energy (from heat inside the Earth), biomass energy (from organic materials), tidal energy (from ocean tides), and wave energy (from ocean waves). These sources are more sustainable and have less impact on the environment compared to fossil fuels.