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 199 potential impact value of moderate and no security objective is assigned a FIPS 199 potential impact value of high. Note: For National Security Systems, CNSSI No. 1253 assigns one impact value (low, moderate, or high) for each of the three security objectives (confidentiality, integrity, and availability), rather than using the FIPS 200 high water mark across security objectives. 
Sources:
CNSSI 4009-2022 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 800-60 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