What does shade, sun to part sun mean?

Very good question!

It has to do with time. Full sun means that the sun shines on the spot from first light till dusk, about 10 hours of sun in the summer.

Part sun is less than that. There's a tree or a fence or other structure in the way shading the plot for a few hours.

Part shade to shade is where you only get an hour or two of direct sun on the spot each day.

Full shade? Dunno. Dappled shade is where you have spots of light that hit the forest floor and move around during the day.