In reference to a track coppers represent the weight of the track. The more complex the blocks and terrain get, it gets harder on your system, and therefore heavier. This number is usually found in the editor in one of the corners of the screen. When you first open up a new track, you'll see a number that I think is between 1000 and 2000. As you place blocks, you can watch it go up. Tracks with an extremely high amount of coppers will often result in poor framerates on older systems.