It's interesting to see different definitions people have for middle class. I suspect this poll's definition includes a lot more people than you might think and it is a way to avoid saying that the middle class is shrinking and more people's wages/salary/benefits are not sufficient to accumulate significant savings or property (working class, imo).
This poll:
Americans who are considered “middle class,” earning above 200 percent of the federal poverty level (FPL).
This is $2500/mo for a single person, or $5000/mo for a family of 4, across the US. Where I live, this would barely meet the definition below.
The Economist:
beginning at the point where people have roughly a third of their income left for discretionary spending after paying for basic food and shelter.
By this definition, they estimated half the world was middle class in 2009. Discretionary spending is health, savings, transportation, education, "a fridge", clothing, care of children or disabled family, etc.
Bourgeoisie:
the owner of a small-to medium-sized business
American Dream:
Likely to own a home (paid off) by the time they are 60.