A batch is a special function of a course. It is a group of users who are allowed to take or see a course at a particular time.
You must create batches for different groups with different schedules for taking the course.
Once the batches are ready, you can control their access period for a course. You can also add or remove certain users from the batch even while the course is ongoing.
Related Article:
Setting Up a Batch - https://support.castlms.com/help/setting-up-a-batch