A group of fish swimming together is commonly called a school. The term "school" typically refers to a coordinated group of fish that swim in the same direction, moving in unison. Schools can vary in size from just a few fish to thousands, and they often function as a survival strategy to evade predators. Certain species of fish, like sardines and herring, are more commonly seen in schools, and this behavior can enhance feeding efficiency and reproductive opportunities. The stunning visuals of schools in action are often a highlight for divers and marine enthusiasts.