Depends who you ask, or the context. Anecdotally, software developers, being more math-minded than average, tend to think of middle-class literally - the middle third or middle quintile of income distribution.
I agree. I was just pointing out that there is a portion of the HN readership that tends to use the strictly economic definition (rightly or wrongly). Also, the meaning has shifted over time.
As used in the early 1900s - I realize the term was coined even earlier than that - it referred to what today we'd likely call upper-middle-class (or if you're a fan of Engles, the bourgeoisie). White-collar, professional, well-educated, but not rich/powerful/nobility. It excluded almost the entirety of the working-class (even those who, by income, were well above poverty).
More recently, usage in the US has trended towards anybody above poverty but not quite rich (and choose your own definition of rich to suit your point). Which itself includes a massive span of incomes and lifestyles.
