The main differences between prequalification, pre-approval, and a mortgage application are the level of detail, the amount of time involved and the impact on your credit score: 

• Prequalification: An informal step that provides a general idea of how much you can borrow and what your monthly payments might be. It's usually a fast process that involves a credit check to display your external mortgages, loans and lines of credit. It’s not a credit application and won’t affect your credit score. 
• Pre-approval: A more in-depth process that involves a credit check and a formal mortgage application. It provides a more precise estimate of how much you can borrow, and locks in the rate so that if your mortgage interest rate goes up, you’re protected for the rate hold period. 
• Mortgage application: The official application that you must complete to get approved for a mortgage. It involves a credit check and a formal mortgage application, as well as providing details about the property you wish to purchase or refinance.

Note: Pre-qualification and pre-approval are not guarantees that you'll be approved for a loan, but they can help you determine how much you can borrow and what to look for