You have enabled Two-Factor Authentication. There are a few
important changes you need to be aware of:
You will need your second factor, along with your primary password,
to access this account management interface.
You will no longer be able to log in with standalone clients for
non-web services using just your primary password. Instead, you
will need to set up Application-Specific Passwords for
non-web clients.
Thank you for taking these steps to protect your account!