Solipsism is the philosophical theory that what's in your mind is the only reality that can be known and verified.
Solipsism comes from the Latin words for alone (sol) and self (ipse), and means that only the self is real. In metaphysical solipsism, your mind is the only thing that's real, and everything else is just a representation. In epistemological solipsism, there might be a world outside your mind, which you could detect with your senses, but it's impossible to prove. In methodological solipsism the self is the only proper starting point for exploring the nature of reality.