A Denial of Service (DoS) attack 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. In a typical DoS attack, the attacker uses a single computer and internet connection to send a large volume of requests to the target. More complex variations, known as Distributed Denial of Service (DDoS) attacks, involve multiple compromised systems working together to amplify the attack, making it even harder to defend against.