Infill in its broadest meaning is material that fills in an otherwise unoccupied space. The term is commonly used in association with construction techniques such as wattle and daub, and civil engineering activities such as land reclamation.
Suburban infill describes the development of land in existing suburban areas that was left vacant during the development of the suburb. It is one of the tenets of the New Urbanism and smart growth trends of urging densification to reduce the need for automobiles, encourage walking, and ultimately save energy. One exception to this is the practice of urban agriculture, in which land in the urban or suburban area is retained to grow food for local consumption.
The Village of Ponderosa in West Des Moines, Iowa is a good example of suburban infill. It was formerly a 9-hole golf course surrounded by suburban West Des Moines businesses and tract homes, but starting in 2006 it was redeveloped into a high-density mixed-use community with a pedestrian friendly retail center.
The advantage of infill housing is in the fact that it does not require the subdivision of greenfield land, natural areas, or prime agricultural land. Another advantage is that existing infrastructure is usually almost adequate to provide all the need for utility and other services, at least at first glance.
A possible disadvantage is that structures built as infill may clash architecturally with the older, existing buildings.