What does the term "real estate bubble" mean?

What does the term "real estate bubble" mean?

John Caliendo (Realtor) gives expert video advice on: What are the common reasons for buying a second home?; If I am buying a second home as a rental, what factors should I consider?; If I am buying a second home as a weekend getaway, what should I consider? and more...

When buying a second home, a real estate bubble is a hot topic in many cocktail parties that I attend; it basically refers to a market being over-inflated by an overzealous buying public who are artificially inflating home prices to the point that they will ultimately have to implode. Now, whether or not this is the reality of real estate, it remains to be determined. To answer the question, what is a real estate bubble, that answer would probably be a good description.