epair(4) on FreeBSD
The text 383422a2ed3b, as FreeBSD 14.3-RELEASE, FreeBSD 14.2-RELEASE, FreeBSD 14.1-RELEASE, FreeBSD 14.0-RELEASE, FreeBSD 13.5-RELEASE, FreeBSD 13.4-RELEASE, FreeBSD 13.3-RELEASE shipped it.
A pair of virtual back-to-back connected Ethernet interfaces