On Linux, administrators may use a service manager such as systemd to request a reload. The service decides what that operation actually does. Some programs reread configuration in place; others start new worker processes and let old ones finish current requests.
Reload and restart are not interchangeable promises. A reload may preserve active connections, but a service might not support it at all. The operation also does not necessarily replace every old executable or loaded library after a binary security update.
That distinction is important for PHP-FPM and related web services. A configuration-only change might need a reload, while a vendor update could require a full restart or redeployment to ensure all running code is current.
Read the service's documentation and the package advisory before choosing. Validate configuration first, observe the resulting processes and confirm the expected behavior with a request to the real application.