Basically, when StackOverflow goes offline, the server puts up a static webpage telling us all that it is down for maintenance.
Then, the server searches through its database and absorbs some of the awesomeness that Jon SkeetJon Skeet has rubbed off on the website and uses it to make changes that benefit the website.
$('#jon-skeet').absorb();
The problem is, too much of a good thing can be bad. So just before the server absorbs too much of Jon's awesomeness, it stops and comes back online. It will then repeat this process a week or two later.