The "5" means to wait 5 seconds before redirecting. The "html-redirect2.html" after "url=" is the URL of the page to which to redirect.<META HTTP-EQUIV="Refresh" CONTENT="5; URL=html-redirect2.html">
These two pages, "html-redirect.html" and "html-redirect2.html", will continue to switch back and forth until you close the window.
It is customary to include a direct link to the page that will be switched to automatically in case you get an older browser that doesn't support the feature or the user doesn't want to wait. Something like:
This page has moved. If your browser doesn't automatically redirect to its new location, click here.