What is a 'botnet' and how does it relate to DDoS attacks against Xbox Live?

A botnet is a network of computers infected with malware and controlled remotely by an attacker. These infected computers, or 'bots,' are used to launch DDoS attacks. Attackers often target vulnerable devices (like IoT devices or even compromised computers) to build botnets, which can then be used to flood Xbox Live servers with traffic.