GLE (ground level enhancements) are sharp increases in the ground-level cosmic ray count as observed at a number of stations worldwide. Thought to be triggered by the arrival of solar protons of energies greater than 500 MeV. These relatively infrequent events are primarily seen as an increased flux of secondary neutrons which may last from 10's of minutes to hours after the flare's maximum.
Forbush decreases are abrupt drops in the background cosmic ray flux due to magnetic field increases in the solar wind. Typically seen at ground level as a decrease in the secondary neutron count. See the NGDC site (linked above) for more information.