Procedural in this case means the actual resolution is calculated in relation to the distance to the camera. Means? Close parts of the terrain will have a very fine resolution when rendering, more far away parts have a lower one. With that you can do a whole landscape with only one terrain if you like. In difference to that normal terrains have only one user defined resolution. If you go to close you'll see jaggies probably.

One day your ship comes in - but you're at the airport.