By TheStreet Staff What Is a Market Bubble?The old saying goes “you never know you’re in a bubble until it bursts,” and that is especially true in the stock market. A bubble is defined as a period when prices rise rapidly, outpacing the true worth, or intrinsic value, of an asset, market sector, or an entire industry, such as real estate. If you’ve ever watched a child blowing soap bubbles, you know how fragile they are. Made from the thinnest film of soapy water, they’re filled with nothing but air, and so any change or sudden movement, from a gust of wind to a curious touch, will cause them …