The 1003 is the mortgage loan application; the 1008 is the underwriter's summary of loan qualification.
The "1003" is a common term used to reference the Uniform Residential Loan Application (URLA), more commonly referred to as a mortgage loan application. The "1008" is a form used to reference the Transmittal Summary, which is primarily used by underwriting for reviewing loan qualification.
The 1003 form is the basic loan application you fill out when applying for a loan. It includes all your basic information, intended loan structure, employment history, income, assets, etc.
The 1008 Form summarizes all the qualifying figures on a loan application (debt, income, loan terms, etc.) to help the underwriter quickly review a snapshot of qualification.