Strong authentication refers to the authentication process that confirms the user's identity beyond a username and password. Strong authentication enables secure access to online systems, applications, and devices. Some synonyms of strong authentication include multi-factor authentication, two-factor authentication, or multi-step verification. Multi-factor authentication involves using different methods of authentication, such as a password, fingerprint, or token. Two-factor authentication combines two types of authentication, such as a password and an SMS code. Multi-step verification adds additional authentication steps, such as a security question or biometric authentication. Strong authentication methods provide greater security beyond traditional username and password, keeping sensitive data and systems safe from unauthorized access.