This is a difficult one. In the urban planning field, “affordable housing” means quality housing that a household can afford, regardless of their income range. “Affordable housing” for a middle class American household means they can reasonably afford the rent or mortgage payments, plus utility and maintenance expenses, for a typical 3 bedroom, 2 bathroom house with few deficiencies. However, many use the term to mean “income qualified housing”, “subsidized housing”, or “workforce housing”.
I have to be very careful about how I use the term “affordable housing” in my work. I live and work in an area with where a middle class household can more-or-less afford a median-priced house $200-$250K house, but that money gets you something that’s very “rustic” by American standards. We’re talking an on-frame modular house that’s essentially a double-wide mobile home, a 1100’^2 / 100m^2 1950s ranch that’s a time capsule, or the region’s modal house – a gabled ell “folk Victorian” that would be functionally obsolete by American standards . Ancient kitchen, fridge in the hall, main bathroom off the kitchen or living room, 7’ ceilings, no level floors or right angles anywhere, etc. I might say there’s a lack of “quality affordable housing”, and people understand that in a context that’s different than “subsidized”. If I say a project will have “affordable housing”, though, my audience will assume it’s income-qualified / subsidized / LIHTC (Low Income Housing Tax Credit), intended for low/moderate income households.