In a nutshell, it is what it says. In order to use a program or log in somewhere, you need to use your regular password and then there is a secondary (or sometimes more) authentication method.
The big third party dual factor authentication out there is Duo. You set up a Duo account and then put the app on your phone. Then you tie Duo to a certain program and then when you log in to that program, you also need to accept the authentication that Duo provides. This is a great way to deter hackers and other intruders.
Office 365 provides multi factor authentication. Gmail provides it as well. A lot of companies are moving to dual/multi factor authentication as an option. We recommend it. It’s just another tool in our inventory to provide you the best solution.