Okay, hang on...

There are single-sided pedals that you'd see on road bikes -- Look Keo, SPD-SL, etc. There's really only one side to put your feet on regardless of what shoe you have.

There are pedals with a clip on one side and a platform on the other. Are these "double sided", or should they be called "dual purpose" instead?

The reason being, there are other pedals that have clips and platforms on both sides, like that Nashbar pedal linked above, or some Shimanos and all Crank Brothers pedals. There's no "wrong side", no reason to flip them. Those are what I'd call "double sided".

(add-on edit) Of course, there are also Crank Bros. Eggbeaters, which are basically "four-sided"..