In practical terms it means, they've simulated as if billions of people are trying to use the site at any moment, so of course the servers can't cope. Sadly it'wels much easier to destroy something than it is to create it.
And finally a word to those who are attacking the site. Millions use this site, many rely on it for crucial info to make their lives better; some are desperate for help with their debts, and others want support through a myriad of issues. What you're doing is hurting many people, please stop.
WhiteTruckMan You must have just got on the page with that statement on it .