A crepe is simply a thinner version of a pancake. However it is how this thinness is achieved that is important. A quick look at the difference between recipes soon shows how this difference is achieved.
A crepe recipe is identical to a pancake recipe in all but one regard. Crepe recipes have higher ratio of liquid to flour then the standard pancake recipe will do. So why is this?
There is actually a very rational reason for this minor difference. Crepe batter needs to have a high liquid content so that it spreads in an even thin layer over the cooking surface so that the resulting product is thin enough to be easily rolled. Where as Pancakes are know for being thick and fluffy - this can be achieved with a thinner batter, but it easier to work with a thicker batter for nice pancakes.
Disgustingly simply reasoning, huh? The good news is that if you find a pancake recipe you want to try as a crepe its simple to alter it too make crepes.