An authentication code is a unique sequence, often generated dynamically, used to verify a user's identity during login or sensitive transactions. It acts as a security measure to ensure that only authorized individuals can access specific systems or perform certain actions. Authentication codes are commonly used in two-factor authentication (2FA), where users receive a one-time code via SMS, email, or an authenticator app. These codes are typically valid for a short period and become invalid after use, reducing the risk of unauthorized access. By requiring an authentication code in addition to a password, organizations significantly enhance their security posture against threats such as phishing and credential theft.