Actually, the orca is a kind of oceanic dolphin. It's just a very unusual dolphin because it is so large. When you look at the classifications on the Orcinus orca page, you will see that this species' placement within the family Delphinidae (the dolphins) is undisputed. Within toothed wales (Odontoceti), the use of common names can be a bit confusing. Basically, they are all whales, but many of the smaller species are called dolphins in the vernacular.