Midtown is the part of a city that sits toward the middle — near the centre, but in the tidy dictionary picture not the main business core. American English uses it most. Though actually, in New York, the city that made the word famous, Midtown Manhattan is the busy office-and-theatre belt: Times Square, big shops, tall buildings. Downtown there is the older financial tip of the island, and Uptown is further north. So midtown does not always mean 'not the main business area'; in New York it often is the main business area, just not the Wall Street end. In other US cities, Midtown can simply be a neighbourhood name for a district beside downtown. British English hardly uses it; we more often say the centre, or a district name. Neutral to informal. You see it on maps and in 'Let's meet in midtown.'