Browser
ERR_CONNECTION_TIMED_OUT The connection timed out
What it means
The browser tried to open a TCP connection and did not get a response in time. The name may have resolved to an address, but nothing usable answered on the port, or a filter dropped the traffic.
Where you usually see it
Sites that are down, addresses that no longer point at a live machine, and networks that block a port. It also appears when a firewall on your side silently drops the attempt.
What to try first
Check whether other sites load, and whether this site loads on another network (a phone connection, for example). If only one site fails, it is probably that site or a filter aimed at it. If everything fails, look at your own network first.
When to stop
A timeout is not proof that the site has vanished forever, and it is not a reason to install a "cleaner" program. If you run the server, confirm that it is listening on the port and that a firewall in front of it allows the traffic.