Recently, we’ve seen stock prices shoot up, with home prices following right along. As they’ve risen higher and higher, some market watchers have tossed around a word that connotes something very light, but in this context, carries heavy meaning: bubble.

“A bubble is one of these things like pornography, you know it when you see it,” says Allan Sloan, Fortune’s senior editor-at-large. “To me, a bubble is an Internet stock that comes out at $40, goes to $100, and two years later trades at $7. But these days, a bubble seems to be defined as something that will go down.”

To hear more about whether we are in a housing, stock, or even a bond market bubble, click on the audio player above.