DoS stands for "Denial of Service". It is a type of attack where an attacker attempts to make a website, server, or network unavailable by overwhelming it with traffic or requests. The attack is typically carried out using a single computer or device that sends a large amount of traffic to the target. This flood of traffic can overload the target system's resources, making it unavailable to legitimate users.

DDoS stands for "Distributed Denial of Service". It is similar to DoS, but it is carried out using a large number of computers or devices that are distributed across the Internet. The attack is coordinated by a command and control server, which sends instructions to the compromised computers or devices to launch an attack against the target. The goal is the same as a DoS attack, which is to overwhelm the target system with traffic and make it unavailable to legitimate users.

The main difference between DoS and DDoS is the number of computers or devices used to carry out the attack. DoS attacks are carried out using a single computer or device, while DDoS attacks are carried out using many computers or devices that are distributed across the Internet. As a result, DDoS attacks are typically more difficult to defend against, since they can come from many different sources and are often harder to trace back to the attackers.