A lockout is a security control that temporarily or permanently blocks account access after too many failed logins, suspicious activity, or other policy triggers. It is meant to slow guessing attacks, stop automated credential stuffing, and force review when an account starts behaving abnormally. In practice, users may suddenly lose access to a mailbox, VPN, firewall console, or admin portal until the account is reset or the limit expires.
Lockouts matter because they are both a defense and a signal. For defenders, they can contain abuse by cutting off repeated authentication attempts. For attackers, they may reveal that stolen passwords are being tested or that valid credentials are being used from an unusual location or device. In perimeter systems such as firewalls, a lockout can be an early warning that administrative access is under attack, so operators should investigate the source of logins, review alerts, and confirm whether the event was caused by brute force, misuse, or a legitimate user error.