When someone reports to me "The website is down" I roll my eyes and immediately seek more information. I wrote up information below, imagining that one day I'd share it with someone reporting that "The website is down". Of course, I probably never will because I try not to be a dick. But I'll share it here:
FYI, "down" has a lot of meanings which most people don't differentiate between when reporting the problem:
1) Site can't be connected to at all (connection timeout), due to one of the following:
a) DNS doesn't resolve to any IP
b) DNS resolves to the wrong IP
c) DNS resolves to the right IP, but the server is powered off or otherwise unreachable over the network
2) Site responds with a connection reset
3) Site responds with "connection refused"
4) Site responds, but is slow to load
5) Site responds but has invalid or misconfigured TLS settings, resulting in the browser showing a security error.
6) Site responds with a server error (HTTP code in the 5xx range)
7) Site responds with a 404 Object Not Found error
8) Site responds with a redirect loop, causing the browser to give a "too many redirects" error page
9) Site responds with little or no content. (Empty page)
10) Site responds with the right content, but it is abnormal:
a) Missing Images
b) Odd formatting (i.e. missing CSS)
c) Some dynamic behavior doesn't work (i.e missing JavaScript)
11) Site responds with other, unexpected content.