Credit is a pay later system. It is an agreement whereby a financial institution agrees to lend a borrower an amount of money over a given time period and whereby interest is typically charged on the outstanding balance.
Credit gives borrowers the ability to purchase goods and services (or for companies, credit gives borrowers the ability to invest in projects) that they normally might not be able to afford. By lending the money, creditors make money by charging interest while helping borrowers pursue their projects. However, as many people have learned the hard way, taking on too much debt can cause a lifetime of damage.