Freddie Mac is a nickname for the Federal Home Loan Mortgage Corporation (FHLMC).  Yes, they are a company, but also a government sponsored enterprise that congress created to keep the flow of credit going (economy) and to reduce risk to investors.  Their existence is a bit complicated, but they basically go out and buy mortgages, then resell those mortgages as a mortgage backed security.  They make their money by charging a fee on the loans they purchased which makes investors assume less risk for spending their own money.  Freddie Mac will guarantee that the loan gets paid back even if the borrower never repays the loan.  Sounds like insurance huh?