Here and in several other documents you see many acronyms that are associated with the notion of a second means of authentication. This is a non-exhaustive list:
| Acronym | Description |
| MFA | Multi Factor Authentication. You will need to identify yourself using an additional, independent from account password, means, such as a 6 digit code or smartphone app |
| 2FA | Instance of MFA with only one additional means of authentication |
| OTP | One time password |
| One time password | A usually additional password that you need to give in order to authenticate and be allowed to login |
| TOTP | Time-based one time password |
| Time-based one time password | A usually addition password, which is valid for a limited amount of time, that you need to give in order to authenticate and be allowed to login |
| HOTP | Event-based One-Time Password |
| Event-based One-Time Password | A usually hardware based additional means of authentication, sometimes implemented using USB keys |
| OATH | Open Authentication TOTP HTOP is a protocol defintion on how to use TOTP (or HTOP) |