What exactly does sola scriptura mean, anyway?

Recent scholars have pointed out that for most historic and contemporary Protestants, sola scriptura does not mean that the Scriptures are the only source of theological truth. They do not see Scripture as sole resource, sole source, sole authority or material sufficiency. Rather, sola scriptura means that nothing other than Scripture properly understood is the final authority or norm for Christian belief. The fact that the Reformers not only appealed to ancient creeds but also wrote creeds to which their constituents must adhere demonstrates that for them there are other sources of authority, but only insofar as they reflect accurately the teaching of Scripture.—Why Church History Matters, page 143