When a wireless signal hits an object it dosen't just stop or bounce straight back it could turn, bend, breakup, slow down, or even turn a corner. If you don't take into account these possible senerios your wireless network could have large big issues that could plague your network.

Scattering: Scattering will take place when a wireless signal hits an object that has many irregular angels causing the signal to shoot off into many directions. This could happen when a signal hits a mountain side, hills or large buildings.

Reflection: Reflection happens when the signal just completely bounces off the object. This can be a good thing and a bad thing. Reflection can be good because clients don't have to rely of LOS (Line or Sight) service. Signals can be trasmitted and bounced off large buildings to a client. Reflection can be bad of it causes signals to bleed into a uneeded area.

ReFraction: Refraction is the bending of your wireless signal as it goes through a medium of higher density than its origin. If you signal has to travel throught industrial areas with smoke stacks valleys with warmer air pockets this will produce refraction.

Absorption: Shoot your signal at a larger brick building and your signal might be sucked up and disappear.

Diffraction: THis is often mixed up with refraction. Diffraction occurs when your wireless signal hits a very large object, slows down and actually turns around the corner. This is great if you want your signal to bend around the corner but if you don't it sucks. Plus it slows down your signal making it weaker.

If you are having problems with weak signals or clients being dropped from the WLAN you could have an Interference due to the above signal behaviors. Also knowing that your signal can reflect or turn corners will help you avoid possible security threats.