What is the National Institute of Standards and Technology (NIST)? 

NIST 800-171 Rev. 2:  The National Institute of Standards and Technology Special Publication 800-171 provides agencies with recommended security requirements for protecting the confidentiality of Controlled Unclassified Information (CUI) when resident in Non-Federal Information Systems and Organizations. There are over one hundred security requirements in the NIST; this document is summary in nature and not an exhaustive list. See the NIST for complete details.