A login is a set of credentials used to authenticate a user. Most often, these consist of a username and password. However, a login may include other information, such as a PIN number, passcode, or passphrase. Some logins require a biometric identifier, such as a fingerprint or retina scan.
Logins are used by websites, computer applications, and mobile apps. They are a security measure designed to prevent unauthorized access to confidential data. When a login fails (i.e, the username and password combination does not match a user account), the user is disallowed access. Many systems block users from even trying to log in after multiple failed login attempts.
At a basic level, logins make user accounts possible. Most systems require unique usernames, which ensures every user’s login is different. On a more advanced level, logins provide a security layer between unsecured and secure activity. Once a user logs in to a secure website, for example, all data transfers are typically encrypted. This prevents other systems from viewing or recording the data transferred from the server.