Variable Frequency Drive (VFD) definition in Computer Security terms:
Definition(s): A type of drive that controls the speed, but not the precise position, of a non-servo, AC motor by varying the frequency of the electricity going to that motor. VFDs are typically used for applications where speed and power are important, but precise positioning is not.
Source(s): NIST SP 800-82 Rev. 2 (NISTIR 6859)
reference: CSRC Glossary