"Bond Basics" and related information;
http://www.investopedia.com/university/bonds/Here's their page on stocks;
http://www.investopedia.com/university/stocks/The following is an excerpt from the "Bond Basics:Yield, Price and other Confusion" page;
Measuring Return With Yield
Yield is a figure that shows the return you get on a bond. The simplest version of yield is calculated using the following formula: yield = coupon amount/price. When you buy a bond at par, yield is equal to the interest rate. When the price changes, so does the yield.
Let's demonstrate this with an example. If you buy a bond with a 10% coupon at its $1,000 par value, the yield is 10% ($100/$1,000). Pretty simple stuff. But if the price goes down to $800, then the yield goes up to 12.5%. This happens because you are getting the same guaranteed $100 on an asset that is worth $800 ($100/$800). Conversely, if the bond goes up in price to $1,200, the yield shrinks to 8.33% ($100/$1,200).
Yield To Maturity
Of course, these matters are always more complicated in real life. When bond investors refer to yield, they are usually referring to yield to maturity (YTM). YTM is a more advanced yield calculation that shows the total return you will receive if you hold the bond to maturity. It equals all the interest payments you will receive (and assumes that you will reinvest the interest payment at the same rate as the current yield on the bond) plus any gain (if you purchased at a discount) or loss (if you purchased at a premium).
As a poster above suggests, when there is a 'Rally on the Bond Market" it is usually as a result of investors seeking a more secure place to invest money when steep declines or market volatility come into play.