A Two Factor Authentication (2FA) Token is an added layer of security for your account that lets your prove you are who you say you are particularly when logging in. A 2FA verification token is generated on your device after enabling 2FA on your Authereum settings page. You can use these codes to log into your account and prove ownership.
A security key (also referred to as a hardware token) is a small hardware device carried by a user to authorize access to a service. The device may be in the form of a smart card or may be embedded in a key fob.
Authereum allows you to choose either of these options when optionally adding more protection to your account.