A banker is a person who carries on the business of banking. This legal definition, from the Bills of exchange Act, is functional rather than circular, because it ensures that the legal basis for bank transactions such as cheques do not depend on how the bank is organised or regulated.
Banks borrow money by accepting funds deposited on current account, accepting term deposits and by issuing debt securities such as banknotes and bonds. Banks lend money by making advances to customers on current account, by making installment loans, and by investing in marketable debt securities and other forms of lending.