Before revision: Metaphysical solipsism is the variety of idealism which asserts that nothing exists externally to this one mind, and since this mind is the whole of reality then the "external world" was never anything more than an idea.
After revision: In metaphysics, metaphysical solipsism is the variety of idealism which asserts that nothing exists externally to this one mind, and since this mind is the whole of reality then the "external world" was never anything more than an idea.