Class II Malocclusion occurs when your upper teeth severely overlap your lower teeth (also known as an overbite). In dental terminology, this is also known as Retrognathism (or Retrognathia), from the Latin prefix Retro (backward) plus the Latin word Gnathous (jaw).
Edward Angle, the father of modern orthodontics, was the first to classify malocclusion types. He based his classifications on the relative position of the top first molar to the other teeth. In cases where the first molars are missing, Orthodontists use canine teeth to determine the relationship.
Illustration courtesy of dentodontics.com