Non-conforming loans do not conform to the qualifications and guidelines set by Fannie Mae and Freddie Mac corporations.
If you require a loan larger than a conforming loan, you will be looking at non-conforming loans, such as Jumbo loans or loans with less stringent guidelines.
These types of loans typically charge a little higher rate, No Mortgage Insurance, and not backed by FNMA/FHLMC. These loans are for people who cannot qualify for conforming loans, need less documents, and scrutinization. The DTI is typically higher and LTV is lower. There are many type of Non-conforming loans, aka ALT-A or Non-Prime loans.