A denial-of-service attack (DoS) is a malicious attempt to disrupt the normal functioning of a targeted server, service, or network by overwhelming it with a flood of traffic. This excessive traffic can prevent legitimate users from accessing the service, effectively rendering it unavailable. Attackers often use various methods to generate this traffic, such as sending numerous requests or exploiting vulnerabilities in the system. In more complex cases, a distributed denial-of-service attack (DDoS) involves multiple compromised computers, often part of a botnet, working together to launch the attack. This makes it harder to defend against, as the traffic comes from many different sources. Organizations like Cloudflare and Akamai provide services to help mitigate the effects of such attacks.