Solipsism is the view that the only things that exist are me and my ideas. Nothing exists outside of my mind.

By the beginning of the third Mediation Descartes is in a solipsitic predicament: He has proven that he exists. He knows with certainty that he is a thinking thing and that he seems to feel heat, etc.

But how can he be certain that there is anything else that exists? How can he refute solipsism? That is his project in Meditation III.