Debt to Income Ratio (DTI)
Used to evaluate likelihood of repayment. This is all of your minimum debt payments added together and divided by your monthly gross income and expressed as a %.
Debt to Credit Ratio (DTC)
Used to evaluate how responsibly one uses their revolving credit. This can be done when evaluating a single tradeline (such as a credit card) by taking the amount used and dividing it by the amount available on the card expressed as a percentage. Combine usage of all tradelines divided by all available revolving credit. E.g. one can have 10% utilization on one credit card, but could also have 80% utilization overall.
FICO Score
A score typically between 300 and 820 (depending on which model is being used). The higher the score, the lower level of risk of loan default is what is predicted.
Of these three terms your FICO score and DTI are the main determining factors for most consumer loans.