Definition
Interest is the cost of borrowing money, paid to the lender over time.
If you are comparing mortgage options, treat interest as one piece of the total cost and risk picture, not a standalone detail.
Why It Matters
Interest matters because it is a major part of the total cost of a mortgage.
Simple Example
A monthly payment often pays interest first, then applies the remaining amount to principal.
How to Use This Term
When you see interest on a loan estimate, calculator result, or lender conversation, connect it to three practical questions: how it affects monthly payment, how it affects cash needed now, and how it affects flexibility later.