Authentication is the method used to verify a user when they are logging into a device, service, website, app, etc. Authentication does not just cover passwords, as you can also use PINs, biometrics, patterns, one time passwords and tokens. Two factor authentication can also be used to add another layer of security. Authentication is there to ensure that only you can access your account.
Sometimes the term multifactor authentication is used to indicate that two or more types of authentication are in use.
National Cyber Security Centre (NCSC):
Authentication is the process of confirming the correctness of the claimed identity.
Authentication (from Greek: αὐθεντικός authentikos, "real, genuine", from αὐθέντης authentes, "author") is the act of proving an assertion, such as the identity of a computer system user. In contrast with identification, the act of indicating a person or thing's identity, authentication is the process of verifying that identity. It might involve validating personal identity documents, verifying the authenticity of a website with a digital certificate, determining the age of an artifact by carbon dating, or ensuring that a product or document is not counterfeit.
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