Renewable energy refers to those sources for generating energy that naturally renew, or replenish, themselves after being used to produce energy. For example, wind creates energy but wind continues to blow, from time to time, in varying degrees, and so it continues to create energy, i.e., it is renewable. The same with solar energy – whenever the sun shines or generates light, it will continue to generate energy. As far as we know now, the sun will always shine somewhere, at some times, and at some intensity. By contrast, oil and gas and peat are non-renewable energies in that once you extract the oil or gas or peat (fossil fuel) from the land or sea, it is gone. It does not regenerate itself, at least in any meaningful time frame.
Besides wind and sun, other renewable energy sources include water (hydro), heat from the ground (geothermal), tides and waves, and plant material (biomass).
Some further ideas to explore on Renewable Energy:
Is nuclear power a renewable energy?
What is the relationship between low-carbon energy sources and renewable energy sources? Is one better than the other? If so, why?
Environmental Protection Agency, Ireland, Viewpoints: “Renewable Energy”
European Environment Agency, “Renewable Energy Sources” and Non-renewable Energy Sources”
See “80% of Energy by 2050 from Renewable Sources” in the Reports section of irish environment (August 2011).