Systemd is trying to stop a service. To do an action to a service (or any unit), it runs a job. The job to stop a service is called a stop job. Once the stop job is taken off the job queue, the stop job is running.

The method of stopping a service is configurable, but the default is to send a kill signal to the MainPID, then wait for the process to exit. If it doesn't, after a timeout, the kill is reattempted with a harsher signal.