An API request used by an application that acts as a bot, independently of any particular user. For example, an application that runs on a scheduled basis and closes issues where there has been no activity for a long time. Applications that use this type of authentication don't use a licensed GitHub account so, in an enterprise with a billing plan that allows a certain number of licenses to be used, a server-to-server bot is not consuming one of your GitHub licenses. The token used in a server-to-server request is acquired programmatically, via the GitHub API.