Orcas are often called killer whales — they certainly have the size to be listed among those massive creatures. However, orcas are not actually whales; they are dolphins (and the largest species of dolphin, at that). Taxonomically, they fall into the Delphinidae family, which are oceanic dolphins. It is theorized that the misnomer was originated by sailors who saw orcas' ferocious hunting of large marine animals and dubbed them "whale killers." Then, the term somehow got flipped around over time.