Glossary

Missing middle housing is a range of house-scale buildings with multiple units—compatible in scale and form with detached single-family homes—located in a walkable neighborhood.

A secondary dwelling unit on the same lot as a principal dwelling unit. The accessory dwelling unit may be occupied by an independent household from that occupying the principal dwelling unit.

Any vacant or underused properties, mostly commercial or industrial, where reuse is complicated by real or perceived environmental contamination. Examples include a corner gas station, an office building with asbestos and lead paint, a closed steel plant, or a former storefront dry cleaning business. Brownfields pose health risks and cause blight and economic and environmental burdens, especially in communities of color and urban areas. 

Source: https://www.epa.gov/brownfields