Badgers usually live in pairs, but sometimes in a clan. A clan usually consists of an adult pair and their offspring from the current and the preceding year.
The clan shares the same burrow, called a sett, and defends the territory around it. The boundaries are marked with heaps of dung and strong scent from musk glands near the anus.
One likely explanation is that access to food can vary widely. The larger the territory, the greater the chance that food will always be available at least somewhere within it. But large territories are difficult to defend, and it is easier to do so with a larger group.