The North End is made up of contiguous urban neighborhoods where existing structures are being knit together with "infill development," which often acts as a catalyst for further neighborhood growth, as it has in spades in Salemtown. For inquiring minds, the best definition of "infill" that I've seen is this: "the economic use of vacant land, or restoration or rehabilitation of existing structures or infrastructure, in already urbanized areas where ... public services are in place, that maintains the continuity of the original community fabric."
What about less urbanized, more suburbanized areas? I am thinking particularly of those suburbs where suburban-style infill occurred 30-40 years ago, such that "urban infill" doesn't currently apply as they undergo urbanization. I grew up in a bedroom community in the Dallas-Fort Worth metroplex. I consider it the classic model of a middle-class suburb, relatively free until recently of urbanization. In fact, when a professional ballpark was built in the 1990s in my hometown, owners enclosed the structure with a high-rise office building in order to create the appearance of a more urban environment, absent the actual city-scape that so many ballparks enjoy: it is suburban hyperreality and a totally unurbanized urban simulation.
Now that the suburb is grown old and urbanization from Dallas and Fort Worth seems to be everywhere in the Metroplex, they are coming up with new terms like "reinfill" to describe the creation of high-density, vertical, multi-family, mixed-use structures and property emerging in classic suburbia. Texas sprawl, having reached its limits, seems to be moving up in the literal sense. And simulation in Arlington seems to be exhausting itself and merging into reality.