Services is just Microsoft's "name" for TSR's, Daemons and other programs that are running usually headless in the background without interactivity.
when you boot your computer, Windows goes through a list of services set to autostart and starts them usually before you login. And when you go to shut down, Windows will try to safely shut down services before powering off. Also why sometimes windows shut down seems to be slow. The more services you have, and the larger those services footprints, the longer they often take to start up or shut down.
in reality, All Operating systems have these background tasks and services that operate without your interactivity.