This is when you take your home mortgage (which isn’t tax deductible) and convert it into an investment loan (which is tax deductible).
If you manage this well and within legal guidelines, you put all of your investment earnings into the investment loan. You are then paying off your mortgage, while paying less on your lending because you can deduct the interest. In addition, your investment should be gaining capital (as should your home).
This is very useful for people who earn enough money to make the deductions worthwhile and to be confident they can ride out potential changes in interest rates.
Get advice from a professional before you make the leap – make sure you are clear about the tax implications and the structures you should use.