The collective noun for a group of whales is a pod. Since many kinds of whales are social, they can often be found in pods made up of their relatives or even unrelated whales.
Whales that are most often seen in pods are toothed whales such as the killer whale. Killer whale pods are led by a matriarch who can live into her 80s or 90s. Their ways of hunting and interacting with each other are extremely sophisticated and complex.
On the other hand, baleen whales such as blue whales are mostly solitary. The exception to this is a mother with her calf.