A common HTTP protocol that implies "Forbidden" access.
Users will receive the error if they do not have proper rights to view the page, such as a backend or admin page for a site.
The server is reachable, but lack of proper credentials forces the server to decline access.
Full list of 403 error codes:
403.1 - Execute access forbidden.
403.2 - Read access forbidden.
403.3 - Write access forbidden.
403.4 - SSL required.
403.5 - SSL 128 required.
403.6 - IP address rejected.
403.7 - Client certificate required.
403.8 - Site access denied.
403.9 - Too many users.
403.10 - Invalid configuration.
403.11 - Password change.
403.12 - Mapper denied access.
403.13 - Client certificate revoked.
403.14 - Directory listing denied.
403.15 - Client Access Licenses exceeded.
403.16 - Client certificate is untrusted or invalid.
403.17 - Client certificate has expired or is not yet valid.
403.18 - Cannot execute request from that application pool.