What's the difference between a "job" and a "service" to systemctl?

root@linuxbox:~# systemctl list-jobs
No jobs running.

root@linuxbox:~# systemctl list-units --type=service --state=running
UNIT                             LOAD   ACTIVE SUB     DESCRIPTION
containerd.service               loaded active running containerd container runtime
docker.service                   loaded active running Docker Application Container Engine
getty@tty1.service               loaded active running Getty on tty1
inetd.service                    loaded active running Internet superserver
ntp.service                      loaded active running Network Time Service
rngd.service                     loaded active running Start entropy gathering daemon (rngd)
serial-getty@ttyPS0.service      loaded active running Serial Getty on ttyPS0
ssh.service                      loaded active running OpenBSD Secure Shell server
syslog-ng.service                loaded active running System Logger Daemon
tftpd-hpa.service                loaded active running LSB: HPA's tftp server
watchdog.service                 loaded active running watchdog daemon

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

11 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.