The job lock feature is among the many ways to customize the scheduling and frequency of your jobs. You can enable this feature on the Job Details tab when creating your job.

A locked job will appear on your Calendar with a small padlock in the upper left corner of the tile. You will not be able to move or reschedule that job until it's been unlocked. 

This is extremely beneficial when creating jobs for customers who can only be serviced on a specific day/time. You can always unlock a job from the scheduling tab within that job.

Note:  Locked jobs will not appear on your list when using the route optimizer or batch reassigning jobs.