What does the term "semi-precious" in gemstones mean?

I'm making jewelry and looking for real stones, and most of them on the labels say semi-precious, what in the world does it mean ? I tried to Google it but didn't get a straight forward answer. So please just let me know what does it mean? Does it mean that the stones are fake? Or is it just a description in what category these stones are ? Like precious - would be diamonds= expensive, rare. ?