If you link your Facebook account to other accounts or access it via a number of devices, eventually one will not be able to perform the two-factor authentication explicit in Login Approvals.
So Facebook have provided App Passwords.

App Passwords:

Simply put, these are passwords that replace the two-factor authentication for certain applications or sites. The process is little more involved though than recent configuration options we’ve discussed.
When you select the Generate app passwords, Facebook gives a nice reminder screen before you can continue.

Continuing though we now name the application for which we are creating a password.

Continuing we are presented with a random, horrible string. No, you can’t choose one of your own and no you can’t edit it. It’s like that for a reason.

You can continue to create passwords or return to the Security Settings screen. Here you’re presented a ‘handy‘ reminder by Facebook.

So, to remove or generate more passwords, go to the page you were just on – when you were, umm, generating a password.
Weird…