systemd is responsible for initializing and managing daemons and services
initialize daemons and services at various machine states (most commonly power-on but also power-off, user login, user logout, machine crash, kernel panic, etc)
manage ongoing services & daemons
handle service & daemon dependencies
directly control services & daemons
initialization system
systemd
Init V
daemon: computer program that runs as a background process
service: computer program that responds to requests from other computer programs
where system daemon and service files live (existing services and daemons)