SMS codes are short numerical sequences sent via text messages to verify a user's identity or provide access to services. These codes are often used in two-factor authentication, where a user must enter a code received on their mobile device to log into an account or complete a transaction. When a user requests an SMS code, the system generates a unique code and sends it to the user's registered phone number. This process enhances security by ensuring that only the person with access to the phone can complete the action, making it harder for unauthorized users to gain access.