It means far more than just an SP Energy (which is good since those are banned in the current TCG format). Special Energies are any Energy that is not a Basic Energy. Basic Energy are the standard Grass, Fighting, Darkness, Metal, Fire, Water, Lightning, or Psychic Energy.
One way to tell apart a basic energy from a Special energy is that a basic energy will not have any text explaining what it does. And Special Energies will usuaully say "Doesn't count as a basic Energy card".