Two closely related terms but significantly different.

A pre-qualification gives you confidence in your property offer.

To obtain a mortgage to purchase property, you need to know how much money you are qualified to borrow. With pre-qualification your lender performs a preliminary evaluation of your ability to pay for a property, and estimates a mortgage amount. Your loan pre-qualification helps you to determine the price range of properties that you can comfortably afford.

A pre-approval gives the seller confidence in your property offer.

With pre-approval your lender does a thorough evaluation of your ability to pay for a property, and can provide you with a written confirmation of the mortgage amount. Most sellers prefer accepting offers from qualified buyers. You want the seller to know that you have the financial ability to purchase the property. By including this pre-approval letter with your offer, you are demonstrating that you are serious about purchasing the property and you are prepared to move quickly. It weighs strongly in your favor.