Whale is a name that is used to refer to many different cetaceans.
The largest living animal in the world is the blue whale (Balaenoptera musculus). It is the heaviest animal to have ever lived on Earth. A blue whale can grow to over 100 feet long and weigh more than 200 tons.
Some animals that are commonly called "whales" belong to the family Delphinidae, or oceanic dolphins, so should really be considered dolphins. These include the killer whale (Orcinus orca), or orca, the melon-headed whale (Peponocephala electra), and pilot whales (genus Globicephala).
Baleen whales make up the clade Mysticeti.
A clade is a group of organisms that share a common ancestor. All of the descendants of that common ancestor belong to the clade.
Instead of teeth, baleen whales have baleen plates - comb-like structures that are made of baleen, a thick, flexible substance that contains keratin, which is a protein that is also found in human hair and nails. Baleen is also known as whalebone.
A baleen whale feeds by filtering food - such as plankton, krill or schools of small fish - through its baleen plates.
The blue whale, the humpback whale (Megaptera novaeangliae) and right whales (family Balaenidae) are baleen whales.
Toothed whales share a common ancestor with dolphins and porpoises.
Together with dolphins and porpoises, they form the clade Odontoceti.
The Odontoceti have sharp teeth, which they use for devouring prey.
The sperm whale (Physeter macrocephalus) is a toothed whale.
Whales, as a group, do not form a clade. The common ancestor of all of the whales is also an ancestor of dolphins and porpoises.
Toothed whales are more closely related to porpoises and dolphins than they are to baleen whales.
Some people say that porpoises and dolphins are toothed whales, and that a porpoise or a dolphin is a type of whale.