DDOS is the acronym for Distributed Denial of Service.
Distributed Denial of Service is a form of cyber attack that renders a device/machine/service incapable of operating as intended.
A DDOS attack works similarly a DOS attack, by disrupting the host/service with a massive of amount of false requests/traffic. By spamming the host with excessive activities, the server overloads and ceases provision. The “distributed” portion of the DDOS refers to the method by which spam is sent to the host server; where a regular DOS attack can come from a single IP address, a DDOS attack utilizes a distributed network of devices to realize itself.