A Distributed Denial of Service (DDoS) attack occurs when multiple computers are used to flood a target server, service, or network with excessive traffic. This overwhelming influx of requests can cause the target to slow down significantly or even crash, making it unavailable to legitimate users. DDoS attacks often involve a network of compromised computers, known as a botnet, which are controlled by an attacker. These attacks can disrupt online services, websites, and applications, leading to financial losses and damage to reputation for businesses and organizations affected by them.