Two-factor authentication (TFA, T-FA or 2FA) is an approach to authentication which requires the presentation of two or more of the three authentication factors: a knowledge factor ("something the user knows"), a possession factor ("something the user has"), and an inherence factor ("something the user is").
Read more about Two-factor Authentication: Background, Possession Factors: "something The User Has", Cost Effectiveness, Market Acceptance, Regulatory Requirements, Product Proliferation, Interoperability of Authentication Mechanisms, Man-in-the-middle Attacks, Market Segments, Examples, Related Technologies