Tropospheric scatter (synonym troposcatter) is the scattering of distant TV and FM radio stations by the troposphere so that they come in further than the line of sight. That brings in the distant fading stations. Sometimes, it may bring in stations up to a hundred miles away.

External Links

http://www.its.bldrdoc.gov/fs-1037/dir-038/_5617.htm - FS-1037C definition of tropospheric scatter.