A group of dolphins, or any cetaceans, is called a pod.
The number of individuals in a pod varies between different pods, and can also depend on the species of dolphin in a group. Bottlenose dolphins normally swim in groups of about fifteen individuals, but the size of a pod often increases in deeper water where there is more open space.
The individuals in a pod work together to hunt and take care of the offspring (a baby cetacean is called a calf). Also, different individuals often create strong social bonds which can last the animals’ entire lifetimes.