It's Eau de Cologne, Eau de Toilette, Eau de Parfum and Parfum (or Extrait de Parfum). I listed them from weakest to strongest in terms of concentration, meaning that out of them all, the Eau de Cologne contains more alcohol than the others.
To specifically answer your question, Eau de Parfum is simply "stronger" than Eau de Toilette. It's all about the concentration.
Hope that helped