A DDoS, or Distributed Denial of Service attack, is when many computers flood a website or online service with fake traffic at the same time, making it too busy for real users.

How it works

Attackers often control a large number of infected machines (a botnet). All those machines send requests to the target server at once. The server becomes overloaded - using up its memory, bandwidth, or CPU - and can't answer normal users anymore.

Analogy

Imagine a small shop with one cashier. Instead of one person asking endless silly questions (like in a normal DoS), now hundreds of people rush in and all shout requests at the same time. The cashier can't serve real customers because the fake crowd takes up all the attention. That's what a DDoS does to a website.