Ionic silver is silver oxide dissolved in water (silver ions). This is what we make with the electrolysis cell. The reducing agent rips the oxygen off the silver oxide and spits out elemental silver particles which agglomerate into larger masses that then float in the water forever. Colloidal silver can also be known as a silver particle suspension or as Kephra says, little nanoscopic balls of pure silver floating in water - nothing is dissolved.
The process we use, if done properly, makes silver particles in the range of 10-15 nanometers which is the correct range for its efficacy as a disease fighter.
And yes, most companies that sell 'colloidal silver' online are really selling ionic silver. If its water clear, it is NOT colloidal silver! Its Ionic (or in lower concentrations like a lot sell - 10PPM - it could be just water as there's no inexpensive way - read expensive lab test - to determine what you're really buying).
Caveat emptor!