A DDoS (Distributed Denial of Service) attack overloads a server with excessive requests, leading to service unavailability. Website owners should invest in DDoS protection, which includes services like a global network capacity of 3 Tbps, comprehensive cloud-based security, and a 99.99% uptime guarantee. The document promotes Dosarrest's DDoS protection services, highlighting their 11 years of experience and 24/7 support.