A DDoS (Distributed Denial-of-Service) attack floods a target server, website, or network with overwhelming amounts of fake traffic from numerous compromised devices (a botnet) to exhaust its resources (bandwidth, RAM) and crash the system, making it unavailable to legitimate users, disrupting services, and causing financial harm. These attacks are more potent than single-source attacks because the distributed nature makes them harder to block, often utilizing methods like SYN floods, DNS amplification, or application-layer attacks to paralyze the target.