Denial-of-service (DoS) attacks are attempts to make a computer or network resource unavailable to its intended users. DoS attacks can be launched from a single computer or from multiple computers working together in a botnet.
There are a number of different types of DoS attacks, but the most common type is a flood attack. In a flood attack, the attacker sends a large number of requests to the target computer or network in an attempt to overwhelm it and cause it to crash.