A search against multiple credit databases to establish the credit worthiness of a client - looking for previous credit references, loan repayment histories etc.
'You can run but you can't hide' - it's the same for the mob and for credit searches. So, whenever businesses or people borrow money, they leave a distinctive trail. This can be 'clean' or 'bad'. A credit search revisits the past history of any applicant for a loan or investment to use it as a basis to determine current suitability.