Synergy, or Autodesk Simulation Moldflow Synergy, is the user interface, UI, for pre- and postprocessing.
The software for model preparation and to show results.
Insight, or Autodesk Simulation Moldflow Insight, is the solver.
(solver in general: http://en.wikipedia.org/wiki/Solver )
Insight solvers comes in three packages:
Standard, Premium, Ultimate
To compare, have a look at:
Hope this clarifies.