What makes a person considered to be scientifically literate?

Good question! Most of those quizzes are designed to make you feel good, rather than measure anything. I guess to be "literate" would require you be able to "read and understand" basic concepts in science and technology. If you can have a conversation about something like alternative energy or the food supply, you are scientifically literate. IMHO

I'd expand that to being familiar with the basic principals of the scientific method; at how hypotheses are formed and tested until they can be called "theories" or that they can be disproved.

You should be familiar with at least the essentials of the major sciences; biology, physics, chemistry, etc. As well, the various "controversies" and be able to recognize psuedoscience and nonsense when you see it.