A DDoS attack (Distributed Denial of Service) involves overwhelming a website with a flood of traffic from multiple sources, rendering it inaccessible to legitimate users. This is achieved through a network of compromised computers, often called a botnet, which can send a massive amount of requests concurrently. The primary effect of a DDoS attack is downtime for the affected site, leading to potential loss of revenue and damage to the brand's reputation. Additionally, it can strain resources and impact the performance of other services, complicating recovery efforts.