Command and Control Center
The command and control center (C&C or C2), is the interface that instructs zombies within a botnet to perform specific tasks. Such tasks can include sending out spam, perform Distributed Denial of Service attacks (DDoS), or send other types of requests.
The C&C interface may be centralized or distributed. In the latter, this is done to make it more robust against intelligence firms and their task to disable the C&C systems.