A debenture is a financial product.  More specifically, it’s an investment product where an investor or investors lend their money out over a fixed term and containing a fixed rate in borrowing costs.  In English, that means money is lent by people who have it to people who need it, but the people who need it can’t pay it back in full or in lump sums other than the agreed upon yearly payment.  So, with a thirty year debenture, the borrower has to pay the agreed upon allotment every year for the entirety of the thirty years.

It’s good and bad for both parties, or pro and con if you like that better.  For the lender, you get steady payments every year that you can count on, and at a rate of interest that’s locked in.  So there’s some security there that the investment will continue to yield the anticipated returns.  There is no change to the interest rate and no change to the term.  And the borrower can’t pay it off early and rob you of potential earnings.  If the interest rates in general go down, your investment is protected and secure because it’s locked in at the fixed rate.