MFA stands for Multifactor authentication, or Multi-factor authentication.
Multifactor authentication (MFA) is a security system that requires more than one method of authentication from independent categories of credentials to verify the user's identity for a login or other transaction.
Source: https://searchsecurity.techtarget.com/definition/multifactor-authentication-MFA

Note, MFA is also refereed to as 2FA or Two Factor Authentication

If you want to 'force' MFA for your users in AWS, you can follow the AWS tutorial:
'Enable Your Users to Configure Their Own Credentials and MFA Settings'
https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_users-self-manage-mfa-and-creds.html
which creates a custom Policy and assigns it to a Group and then a User. 

Users with this Group will be 'forced' to add MFA before they can access resources.
'Forced' is a misnomer though. Once logged in, it may appear that you can do stuff, but most pages show non friendly errors that you do not have access, and what Policy to add to enable access. So IAM admin friendly, but not user friendly. Once you have enabled and logged in using MFA, you will able to access resources. So 'told to' or 'resigned to' would be a better Policy description. It would be nice if there was an official AWS Policy to force MFA and the only screen you saw upon login was that. But oh well, the Tutorial does 'work',  so that's all good.

But, what if when you create the user, you required the user to change their password on initial login.
The Policy listed in the AWS tutorial does not allow the user to change their password if they have not enabled MFA. So a chicken egg problem.  Or an angry user if devops didn't test first, or a frustrated devops if they did test first. 

To allow a user to change their password on initial Login, edit the Policy supplied by AWS.
Simply add the iam:ChangePassword permission to the DenyAllExceptListedIfNoMFA list.

  ...
  "DenyAllExceptListedIfNoMFA",
    "Effect": "Deny",
      "NotAction": [
        ...
        "iam:ChangePassword"
        ...

So now a new user can login, change their password, see a bunch of pages which they can't do anything with (uhg), go to their Security Credentials and enable MFA, logout, login with MFA and then be able to get to work.

 -End of Document-
Thanks for reading