HTTP
500 Internal Server Error
What it means
The server ran into a problem it did not handle. The message is deliberately generic. It does not tell you whether a program crashed, a configuration file is broken, or a backend is down.
Where you usually see it
Web applications after a bad deploy, a failed database connection, or a permission problem on a file the application needs. You may also see it on a page that worked yesterday.
What to try first
Retry once after a short wait, in case the fault was brief. If you only needed to read the page, try again later. If you run the site, look at the application and web-server logs on the host; the useful detail is almost never in the page the visitor sees.
When to stop
A 500 is a problem on the server, not in your browser cache. Clearing cookies will not repair someone else's application. If you do not run the site, the only useful report you can send is the exact URL, the time, and what you were doing.