What is the group name for whales, dolphins, and porpoises?

The group name for whales, dolphins, and porpoises is cetaceans.

Cetaceans are marine mammals belonging to the infraorder Cetacea. The group includes familiar animals such as blue whales, humpback whales, sperm whales, dolphins, porpoises, belugas, and narwhals. Although people often use “whale” and “dolphin” as separate categories, dolphins and porpoises are evolutionary branches within the broader cetacean group.

Living cetaceans are divided into two major lineages. Baleen whales, or mysticetes, filter food from water using plates of baleen rather than teeth. Toothed whales, or odontocetes, include dolphins, porpoises, sperm whales, belugas, narwhals, and beaked whales. Toothed species generally use echolocation to detect objects and prey.

Cetaceans are mammals, not fish: they breathe air through blowholes, give birth to live young, and nurse their calves. Their ancestors were land-dwelling mammals, and fossil evidence shows a gradual transition to fully aquatic life. Mustelids are a mammal family that includes otters, sirenians include manatees and dugongs, and pinnipeds include seals, sea lions, and walruses; none is the correct group here.