Delayed job allows us to run ruby processes asynchronously or in the background. The only time we're using it now is with the mailer. In the controller action, we don't want users to wait on the frontend until the mailer delivers an email, because it's not essential to whatever is happening on the frontend. So we `delay` the delivery of the email, and go to the next step in the action. When we use `delay`, the process is added to a Delayed job table in our database and run, when a server is available.

More info: https://github.com/collectiveidea/delayed_job