DDOS

Denial-of-service-attack (DOS attack) where someone is trying to make your machine or network resource unavailable by temporarily disrupting services of a host connected to the internet.

The hacker tries to overwhelm the servers of a DOS victim. The victim receives a lot of traffic that the server can't cope with and eventually all available resources are used and server crashes.

When the traffic comes from multiple sources then we call it a Distributed denial-of-service-attack (DDOS attack). When DDOS is in action it is impossible to stop the attack by simply blocking a single source.