There is no defined difference. Anyone can name their park what they want.
I have seen "RV Resorts" that were close side by side (sardine as you say) sites. Generally they will have a few more amenities, but don't necessarily count on larger spaces. But I have also seen some that were pretty darn nice.
And I have seen "RV Parks" that were also pretty darn nice. But also some that were barely worth an overnight stay.
It is a******shoot unless you do a lot of advance searching for actual previous user comments. And even then, what one person rates very highly, another warns to stay away.