What's a cache, and how do you clear it?
It’s temporary memory in your browser (desktop, laptop, phone) that holds cookies that websites store there. When you log in to a site (like Disqus) with your user ID/password, Disqus stores a “cookie” in your devices memory so you don’t have to enter that info on subsequent visits to that site. You probably don’t have to log in to FR each time you come here because the FR system embedded a user/password cookie in your computer (or whatever you’re using) when you first logged in. Cookies aren’t permanent. You can go to your browser settings and there’s a link to “clear” cookies and history. When you click on that function...you’re clearing your “cache”. You’ll need to login again, at those various sites.
Clearing your cache occasionally is not a bad thing to do. The cache collects a lot of cookies besides user/password info. It also collects “tracking” cookies that follow you around and send info back to sites that you have visited...about sites that you are now visiting. Advertising tracker cookies are big abusers of this type of “intrusion”.
I am sure there are others here at FR that can explain it better.