Most bonds can be called after a certain time has passed. Althought not all bonds are callable - most are as they provide protection for the issuer. Example, GE issues a 5% bond for 25 years callable after 5 years. When five years has passed, GE can reassess the market. If it thinks or knows that bond rates have dropped (say to 3%) - it could call the 5% bond (pay off those bond holders the face value) and reissue a new bond at 3% - which save them money in the long-run.

Do Bonds ever get repaid early by the company offering them or are they strickly a set interest rate until maturity when the principal is then repaid?

Bonds are issued by public companies, large corporations, municipalities, government agencies etc... to borrow money from the public. The bonds can be traded on the stock market. A commercial loan is a loan from a bank to a business with dictated terms to maintain the loan.