Explanation:

JF stands for journal Folio. This number is entered in ledger at the time of posting the journal transaction in the ledger so that at the time of auditing, the records ledger posting can easily be verified from the journal book.
The journal folio (JF), on the other hand, is the page number of your journal. Both the journal and ledger folio can be numeric or alphanumeric. ... It's usually listed next to the journal folio number in the Folio column. The ledger folio number helps ensure that all entries are accurately posted and recorded.