Phocoena is a term commonly used to describe the genus of porpoises, which belong to the family Phocoenidae. There are several different synonyms that are often used to refer to these aquatic mammals, including the terms porpoise, harbor porpoise, and finless porpoise. While these terms may be used interchangeably, each has a slightly different connotation. Porpoise refers to any member of the family Phocoenidae, while harbor porpoise specifically refers to a type of porpoise that is found in waters near North America and Europe. The finless porpoise, on the other hand, is a type of porpoise that lacks a dorsal fin and is typically found in shallow coastal waters.