A perimeter network or screened subnet separating an internal network that is more trusted from an external network that is less trusted.
Sources:
NIST SP 1800-16B
under Demilitarized Zone
NIST SP 1800-16C
under Demilitarized Zone
NIST SP 1800-16D
under Demilitarized Zone
A network created by connecting two firewalls. Systems that are externally accessible but need some protections are usually located on DMZ networks.
Sources:
NISTIR 7711
under Demilitarized Zone