A bond = a long-term I.O.U, a promise that money will be repaid within a given period of time.
Example — A 10-year bond issued by the Ford Motor Company paying a 7% annual interest rate. You pay $1,000 (the "par or principal value") when the bond is issued, i.e., you lend Ford $1,000. You receive $35 in interest from Ford every six months ($1,000 x 7% = $70 per year or $35 every six months; 7% is the "coupon interest rate"). After the 10-year period (the bond's "maturity"), Ford pays you back the $1,000 you lent it.