How do you define “middle class?”

My wife and I both teach and our combined earnings exceed $50,000 but not above $100,000.  We budget, clip coupons, worry about the rising cost of raising our family, and we often wonder if we are setting aside enough money to ensure a comfortable retirement for ourselves. If the title of this blog is life in the middle class it seems only appropriate to define middle class.  That is a challenge all by itself.  Economist and sociologist alike have tried to define and classify this group for the past 60 years, yet there is still no common agreement.  Wikipedia offers a broad definition of middle class giving an income range from $25,000-$100,000 per household income.  It is commonly agreed though that the middle class account for nearly half of the population of the US.  We are a large group that has the opportunity influence economics, politics, and nearly any other aspect of society.   I think middle class is relative to where you live and what type of income is needed to provide a reasonably comfortable lifestyle.  How do you define middle class and how would you classify yourself?