service/daemon is a program run by the system in the background, as opposed to one started and run directly by the user
service/daemon manager manages a plethora of services

Service Managers - History

Service Managers - Types

Service Managers	Service File Extension	Service File Location(s)	Service Manager Command(s)
SysV	`none`	/etc/init.d/*	service chkconfig
Upstart	`.conf`	/etc/init/*	service chkconfig
Systemd	`.service`	/etc/systemd/system/*	systemctl journalctl
Launchd (macOS)	`.plist`	multiple locations	launchctl