In older literature, the term (commutative) ring spectrum refers to a (commutative) monoid in the stable homotopy category, hence to a spectrum equipped with a product operation, which is associative (and commutative) up to unspecified homotopy.

In terms of modern homotopy theory the monoid structure alone is in general not quite appropriate, since one really needs A-∞ ring struture or even E-∞ ring structure. On the other hand, with a suitably symmetric monoidal smash product of spectra on the given category of spectra, this does follow.