Some adjustable rate mortgages allow the interest rate to fluctuate independently of a required minimum payment. If a borrower makes the minimum payment it may not cover all of the interest that would normally be due at the current interest rate. In essence, the borrower is deferring the interest payment, which is why this is called "deferred interest." The deferred interest is added to the balance of the loan and the loan balance grows larger instead of smaller, which is called negative amortization.
A refinance transaction which is not intended to put cash in the hand of the borrower. Instead, the new balance is caculated to cover the balance due on the current loan and any costs associated with obtaining the new mortgage. Often referred to as a "rate and term refinance."
Many lenders offer loans that you can obtain at "no cost." You should inquire whether this means there are no "lender" costs associated with the loan, or if it also covers the other costs you would normally have in a purchase or refinance transactions, such as title insurance, escrow fees, settlement fees, appraisal, recording fees, notary fees, and others. These are fees and costs which may be associated with buying a home or obtaining a loan, but not charged directly by the lender. Keep in mind that, like a "no-point" loan, the interest rate will be higher than if you obtain a loan that has costs associated with it.