slapd.overlays(5) on macOS
The text d5bb39e3e2c3, as Mac OS X 10.6.8, Mac OS X 10.6.7, Mac OS X 10.6.6, Mac OS X 10.6.5, Mac OS X 10.6.4, Mac OS X 10.6.3, Mac OS X 10.6.2, Mac OS X 10.6.1, Mac OS X 10.6 shipped it.
overlays for slapd, the stand-alone LDAP daemon