What is a group of pigs called?

a sounder.

A sounder is a group of pigs, typically made up of a sow (female pig) and her piglets. The group can range in size from just a few animals to as many as 20 or more. Sounders tend to stick together and are often led by the dominant sow. Pigs are social animals that enjoy the company of other pigs, and being part of a sounder can provide them with a sense of security and comfort. When threatened, sounders can become defensive and protective of their young, and will often use their numbers to drive away predators or other perceived threats.