I have tried to search and haven't been able to come up with an answer. I have been under the impression that by definition, a solution cannot have more than one solvent, since a solvent is what does the dissolving of the other elements and a mixture with two solvents would be heterogeneous rather than homogeneous. Can anyone with a little more knowledge spread some light on the situation? Thanks.
You would be correct there but for practical purposes it is often the case that a different solvent can be used to create a solution with very similar properties.
Officially, if there is more than one solvent solvating the material in question, they are referred to as "co-solvents". I was a PhD chemist at Pfizer for 7 years.
I believe there are cases where you can have individual "solvents", in which something that does not dissolve, but when you mix those solvents, all of a sudden, the solute does dissolve. Thus, you must say you have more than one solvent since each contributes to the solvation
Playing devil's advocate-- you could call a co-solvent a single solvent (albeit with two components). For example, even though 40% EtOH has more than one component-- it remains a single solvent.