The documentation is as follows:
The keys of Jobs and Triggers (JobKey and TriggerKey) allow them to be placed into 'groups' which can be useful for organizing your jobs and triggers into categories such as “reporting jobs” and “maintenance jobs”. The name portion of the key of a job or trigger must be unique within the group - or in other words, the complete key (or identifier) ​​of a job or trigger is the compound of the name and group.
Simply put, name+group It forms a unique key, through which you can update, stop tasks, etc.
Write a simple demo:

           JobDetail jobDetail=JobBuilder.newJob(SimpleJob.class).withIdentity("myjob", "job-group").build();
           CronTrigger cronTrigger=TriggerBuilder.newTrigger().withIdentity("cronTrigger", "trigger-group").withSchedule(CronScheduleBuilder.cronSchedule("* * * * * ?")).build();  
           SchedulerFactory sFactory=new StdSchedulerFactory();  
           Scheduler scheduler=sFactory.getScheduler();  
           scheduler.scheduleJob(jobDetail, cronTrigger);
           scheduler.start();  
           Thread.sleep(5*1000);//
           JobKey key = JobKey.jobKey("myjob", "job-group");//通过name+group获取唯一的jobKey
           scheduler.pauseJob(key);//暂停任务

Other applications of group:
You can get all the jobkeys under it through groupname

  GroupMatcher<JobKey> gm = GroupMatcher.groupEquals("job-group");
  Set<JobKey> set = scheduler.getJobKeys(gm);