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.
This is where URL Aliases come in to save the day.
A URL alias is a user-friendly path that's based more on words than on numbers. The numbered option still remains, and this is how Drupal works in the background, but Drupal will also remember our friendlier URLs as well.
There are a couple of modules that are used to generate paths in OSU Drupal 8. First we use the core Path module. This core module gives us the ability to manually create URL aliases. We also use the Pathauto contributed module to clean up poorly constructed paths and to give us the ability to automate path creation based on token values.