What do the signs of a stock market bubble look like?

The stock market continues to hit high numbers despite the overall economy being uneven, to say the least. And recently there's been a lot of people talking about whether or not we're seeing a bubble in the markets. So what is a bubble? What are the signs that one is developing? And is the market doing anything out of the ordinary right now? Cindy Axelrod, Associate Professor at the Fox School of Business and Deputy Finance Department Chair joins KYW Newsradio In Depth to talk about what's happening on Wall Street, why people are concerned, and to explain the wild ride the stock market has taken over the past year.