IMAP and POP3 are the protocols (type of connection) that your iPad is using to communicate with the email server of your Internet/email Service Provider. IMAP is the more modern way to communicate with the server; POP3 is an older standard, but still used by some.
In this context, ”Native” indicates something that is part of the host system (your iPad) - in this case the Mail App that comes with the iOS/iPadOS Operating System. By contrast, “third-party” would be an App from somebody else - like, for example, AOL.
TraceyLAR is seemingly talking about the “third-party” AOL Mail App - and not the “native” Apple Mail App that is part of your iPad Operating System.
In case my very first reply needs further explanation, if you are using the “native” Apple Mail App (or any other non-AOL Mail App) to retrieve your email - following changes made by AOL, you must now generate a unique password for your Mail. This password will be different to the password with which you sign-in to your AOL account.
You must generate this unique (App Specific) password by signing-in to your AOL account - using your web-browser (Safari?). The instructions for generating the App Specific Password are included in my first reply.