A Distributed Denial-of-Service (DDoS) attack occurs when multiple compromised computers, often part of a network called a botnet, flood a target server or network with excessive traffic. This overwhelming influx of requests can cause the target to slow down significantly or become completely unavailable to legitimate users. DDoS attacks can disrupt online services, websites, and applications, leading to financial losses and damage to reputation. Organizations often implement various security measures, such as firewalls and traffic filtering, to mitigate the impact of these attacks and ensure their services remain accessible to users.