Bond at Par

Par value is the stated value of a bond when it's issued. When a bond trades at par, it trades at its face value, and you get what the coupon says. In reality, bonds almost never trade at par because interest rates go up and down all the time, meaning that investors are willing to pay more or less for a bond based on that. 

Example

A company might seek to raise $10 million. It issues bonds at an 8% compound rate which it is obligated to pay, effectively renting the $10 million for the price of $800,000 per year. After a year, interest rates drop to 5%, and now investors are willing to pay more than face value for the bond because the bonds being issued now have only 5% interest, meaning investors get less for their money. The bond is trading above par. Another year rolls by and interest rates climb to 10%. Now that 8% looks paltry, and if you want to sell your bond, you'll sell below market value (below par). If interest rates hit exactly 8%, you can trade at par, but... don't hold your breath.