This is where you have an existing mortgage loan and you decide to borrow more, either by borrowing more under your existing mortgage loan (a top-up), or borrowing more under a new mortgage loan linked to your existing mortgage loan (a further advance).
The lender will generally review all aspects of the existing mortgage loan and your personal circumstances in order to determine if they will offer a further advance or top-up.
Often this is referred to as a “further advance”