As mentioned before you are probably referring to the debt to income ratio (DTI).
This is comprised of all monthly debts showing on your credit report as well as the Principal, interest, taxes, and insurance (and HOA dues if applicable) and then measured as a % of your income.
For example if you make $4,000 a month and your total payments would be $2,000 then your DTI would be 50%
The importance of this depends on what type of loan programs you are looking at as well as the rest of the credit package. (Assets, FICO score, Loan to value ect)
If you are more specific about the loan program you are looking at I can give you a more specific answer.