Put simply, your credit score is a numerical interpretation of your credit worthiness, and is calculated based on a complex combination of all the information TransUnion holds on your credit report over a 6-year period.

You can also read What can affect my credit score?

Lenders will make their own assessment of your creditworthiness based on how your credit history meets their lending criteria, but generally speaking the higher your credit score the more likely you are to make the agreed payments and therefore be accepted for the best credit deals and interest rates.