An information system in which at least one security objective (i.e., confidentiality, integrity, or availability) is assigned a FIPS 199 potential impact value of moderate, and no security objective is assigned a FIPS 199 potential impact value of high.
Sources:
FIPS 200 under MODERATE-IMPACT SYSTEM

  An information system in which at least one security objective (i.e., confidentiality, integrity, or availability) is assigned a FIPS PUB 199 potential impact value of moderate and no security objective is assigned a FIPS PUB 199 potential impact value of high. Note: For National Security Systems, CNSSI No. 1253 does not adopt this FIPS PUB 200 high water mark across security objectives.
Sources:
CNSSI 4009-2015 from FIPS 200

  A system in which at least one security objective (i.e., confidentiality, integrity, or availability) is assigned a FIPS Publication 199 potential impact value of moderate and no security objective is assigned a potential impact value of high.
Sources:
NIST SP 800-37 Rev. 2 from FIPS 200
NIST SP 800-53 Rev. 5 from FIPS 200
NIST SP 800-53A Rev. 5 from FIPS 200
NIST SP 800-53B from FIPS 200

  An information system in which at least one security objective (i.e., confidentiality, integrity, or availability) is assigned a FIPS 199 potential impact value of moderate and no security objective is assigned a FIPS 199 potential impact value of high.
Sources:
NIST SP 800-18 Rev. 1 under Moderate-Impact System
NIST SP 800-60 Vol. 1 Rev. 1 under Moderate-Impact System from FIPS 200
NIST SP 800-60 Vol. 2 Rev. 1 under Moderate-Impact System from FIPS 200