There’s a big demand for more affordable housing in Charlotte, where rents and home prices have shot up much faster than wages over the past few years: Vacancy rates are lower for older, cheaper apartments than flashy new ones, waitlists for housing vouchers are long and starter homes are snapped up almost immediately. So why aren’t developers building more affordable housing? That was one of the main questions at a candidate education panel hosted by the Greater Charlotte Apartment Association on Friday, where about two dozen candidates for Charlotte City Council turned out to learn some of the basics on a complicated subject. “Affordable housing is one of the topics you’ll talk about a lot,” Bryan Holladay, who supervises the group’s government affairs outreach, told the candidates. The subject is an alphabet soup of acronyms (like NOAH, or “Naturally Occurring Affordable Housing”) and overlapping terms and definitions. Sometimes when people say “affordable housing” they mean government-subsidized, while others might mean market-rate housing that someone can afford for 30 percent or less of their income.