Reverse and adjustment postings can also be marked as negative postings. Negative postings are used to reduce the transaction figures in G/L, customer, and vendor accounts. This allows you to give the transaction figures (following the reversal) the status they would have had without posting the reversed document and its reversal document. This type of reversal is called a negative posting. Its nothing but an adjustment. Lets say you have creates a bill of 10 bucks and latter you realize its not correct and the billing amount should be 8 bucks. To change the billing amount you have to create a negative bill worth -2 bucks. Its a negative bill or in other words its an adjustment of credit type. Similarly debit type adjustments are also there.