The United States Environmental Protection Agency (USEPA) defines a Brownfield as: "With certain legal exclusions and additions, the term "brownfield site" means real property, the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant."

Brownfield sites are often vacant, abandoned pieces of land, shuttered by a previous owner or environmental issues posing too many challenges for redevelopment and new operations. Sites fall into disrepair, often resulting in unsafe building conditions, blight, and illegal entry and dumping.

Examples can include dry cleaners, scrap yards, printing shops, schools, auto dealerships, filling/service stations, lumber yards, foundries/factories, and bulk petroleum plants.