What is Cut-off Date?
Cut-off Date meaning The date that determines whether a preference immigrant visa applicant can be scheduled for an immigrant visa interview in any given month. When “C” (meaning Current) is listed instead of a specific date, that means all priority dates are eligible for processing. The cut-off date is the priority date of the first applicant who could not be scheduled for a visa interview for a given month. Applicants with a priority date earlier than the cut-off date can be scheduled. However, if your priority date is on or later than the cut-off date, you will need to wait until your priority date is reached (becomes current). To find out whether a preference case can be scheduled, see the Visa Bulletin.
reference: U.S. Visas – Glossary