Final answer:
A brownfield is an underused or abandoned urban area with environmental contamination, often caused by poor agricultural practices and increased need for food production. The term stands in contrast to 'greenfields,' which refers to undeveloped, unpolluted land.
Step-by-step explanation:
A brownfield refers to an abandoned or underused urban area where redevelopment is complicated due to real or perceived environmental contamination. These sites often have various pollutants such as pesticide resistance, increased salts in the soil, and nutrient-poor soils, which may lead to blight or desertification. Brownfields stand in contrast to greenfields, which have not been developed before and are free from pollution. Poor agricultural practices and the desire for increased food production have sometimes led to land degradation and brownfield formation. Notably, the 'Green Revolution' increased food yields but also contributed to such environmental issues.