Need to replace tire on Dahon folding bike
The Dahon Vitesse D8 site says it ships with


  KOMMUTER, 20" x 1.75"


tires.

Any tires of those dimensions will do the job.

The applications you mention suggest that a tire with a small amount of tread would be better than a slick (no tread) tire.

The mind boggling array of tires you see is because the suppliers are all trying to distinguish their products, when they all do pretty much the same job.

I recommend taking your bike to your LBS and fit whatever tires they suggest, provided they have tread.