NIST SP 800-116
Controller (or Control Panel, or Panel)- A device located within the secure area that communicates with multiple PIV Card readers and door actuators, and with the Head End System. The PIV Card readers provide cardholder information to the Controller, which it uses to make access control decisions and release door locking mechanisms. The Controller communicates with the Head End System to receive changes in access permissions, report unauthorized access attempts and send audit records and other log information. Most modern controllers can continue to operate properly during periods of time in which communication with the Head End is disrupted and can journal transactions so that they can be reported to the Head End when communication is restored.
NIST SP 800-82 Final Draft
Controller - A device or program that operates automatically to regulate a controlled variable. [ANSI/ISA-51.1-1979 - (R1993) - Process Instrumentation Terminology.]