Protective Distribution System definition in Computer Security terms:
Definition(s): Wire line or fiber optic system that includes adequate safeguards and/or countermeasures (e.g., acoustic, electric, electromagnetic, and physical) to permit its use for the transmission of unencrypted information.
Source(s): NIST SP 800-18 Rev. 1
NIST SP 800-53 Rev. 4
reference: CSRC Glossary