Reddit runs a network of user created communities, each organised around a topic and moderated by unpaid volunteers drawn from its own members. Posts are ranked by votes rather than by an editorial team, so what surfaces on the site is decided by the people using it. Advertising sold against those communities provides most of the revenue, with a smaller contribution from licensing the site's archive of human written discussion to companies training language models. Because much of its traffic arrives through search engines looking for opinions rather than official answers, the business is unusually exposed to changes in how those search engines rank and summarise forum content.