Renewable energy defined

How is Renewable Energy defined? Well I never really heard it put in a quantifiable light before, so I tooled on over to Wikipedia to see what it had to say. Of course it includes things such as wind and solar, that was a no brainer. But it also includes things such as rain, tides, and geothermal energy as well. I would suspect it would also include biomass energy. If anyone knows of a renewable energy source that I have not included, by all means leave me a comment.