A DDoS attack (Distributed Denial of Service) impacts online services by overwhelming a target server or network with a flood of traffic, rendering it incapable of handling legitimate requests. Attackers often use a network of compromised devices to generate immense traffic volumes, disrupting service availability. This can lead to significant downtime, loss of revenue, and damage to brand reputation for businesses. DDoS attacks exploit vulnerabilities and can target various services, emphasizing the need for robust cybersecurity measures to mitigate potential threats.