Your backup cycle is set up by your Field Engineer (F.E.) in Function MBC (Backup File Maintenance).
The backup cycle tells the system the rotation of the backup tapes, so it knows which backup tape to request during Backup. For example, your company might have a different backup tape for each day of the week, or three to four tapes that are used on a rotating schedule throughout the week. CDs and USBs are labeled on the fly, so as long as the current backup is not inserted into the drive the CD/USB will automatically have the correct label.
Although your F.E. is responsible for setting up MBC, you may still have occasion to use it— for example, you may need to modify it at some point, or you may need to simply refer to it for information, such as the date of your last successful backup.