An individual's credit score is the assessment by a particular lender of their credit risk (ie how likely they are to repay a debt), generally based on a combination of their credit report compiled by a Credit Reference Agency (CRA) and the lender's own criteria.
A default refers to the closure of an individual's credit account by a lender due to missed repayments. This includes failed payments of utility bills or mobile phone subscription plans. Any defaults affect an individual's credit score and remain on their credit file for six years from the date of default.