Students go to school to learn and, guess what, have some social life! But you know what is even more surprising? That fish and some mammals that live under water also want to have some form of social life! They set up big groups and swim together, they feel safer then (because, obviously, it is more difficult to attack a group than an individual!) and, most probably, satisfy their social underwater needs! Those gropus of fish, whales or dolphins are called schools!.
Example: a large group of fish, dolphins, whales etc. swimming together
Definition:Look! A school of dolphins!