A group of bass is called a school, the standard term for one of the most popular freshwater sportfish in North America. Bass, whether largemouth, smallmouth, or striped, are ambush predators that typically hunt alone, but they do gather in loose schools around structure like submerged logs, rock piles, and weed beds, especially younger bass seeking safety in numbers.
Schooling behavior in bass tends to shift with age and season. Juvenile bass school more consistently as a defense against predators, while adults become progressively more solitary and territorial as they mature, staking out and defending a favorite ambush spot.
Bonus fact: bass have excellent low-light vision and often feed most actively at dawn and dusk, which is exactly why serious anglers plan their trips around those hours.
Bass are also sometimes described using the general term shoal, shared broadly across freshwater fish species.
Related: Collective Nouns for Fish · What Is a Group of Bass Called?