When content is created in Drupal, there needs to be a path built so that we, as humans, have links to follow.
By default, Drupal takes the base URL of the site and appends an entity id path to the base. For nodes, the path is node/123, for terms it's term/123, for users it's user/123, etc.
This is simple and easy for a machine. For people, though, it can get pretty overwhelming quickly as the content starts to stack up.