Sort of.
Diffraction refers to the process by which radio waves "bend" as they pass over physical objects, in this case, terrain. The most commonly seen example that demonstrates this effect is to watch a wave on a lake as it passes the edge of a solid object, for example, a seawall. The area behind the seawall will exhibit some of the wave action but those waves will be heading in a different direction than they originally traveled.
http://www.hdtvprimer.com/ANTENNAS/siting.html shows an illustration that will also show the effect of this bending of radio waves.
In the TVFool analysis, a 1-edge path indicates that there is one terrain obstacle that the signal must bend over. A 2-edge path indicates that there are two identified terrain obstacles which effectively means the signal is bent a 2nd time after it has already been bent previously.
Because of this diffraction effect, signals will be 1) far weaker and 2) scattered (layered) than they otherwise would have been if there had been a line-of sight signal path. That usually means that a greater measure of patience and perseverance is signal hunting is needed and that avoidable mistakes be avoided.
Best of luck!