DOS is the acronym for Denial of Service.
Denial of Service is a type of cyber attack that renders a device/machine/service incapable of operating as intended.
A DOS attack works 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. DOS attacks are an older form of attack and have evolved into DDOS attacks, “distributed” denial of service attack. Where a regular DOS attack can come from a single IP address, a DDOS attack utilizes a distributed network of devices to realize itself.