Scenery, mesh, terrain question

Hello everyone. I am relatively new to the FS scene (pun not intended for this question ). I was wondering what the difference is in scenery, mesh, and terrain. Well, I think I know what scenery is, that would be the 3d stuff at airports and such, right? Well, basically I like to fly around in the Cessna checking out the sites and quite frankly, it all looks so horrible if you aren't at a big city or something. From what I've figured out/guessed at, is that mesh is the elevation data, am I correct? Like I've been checking out this stuff http://www.simviation.com/fsdterrainsrtm.htm which is said to be "70m Global Terrain Mesh for The Whole World"
by Stephen Rothlisberger. I really don't see much of a difference in the look with this. What I'm looking for is what to get to make the terrain look more photorealistic, and I mean all the terrain, not just scenery at certain areas. Is this possible with freeware? Is there anything out there to make it look better, or is the big blotchy texture all I get unless I'm at a detailed city or airport? I am running with everything in the settings maxed btw.

Thanks for any responses

Mike