Greenfield land is a term used to describe a piece of undeveloped land, either currently used for agriculture or just left to nature.

In town planning for new buildings and estates the change of use often gives rise to strong argument about the need to use such a greenfield site as opposed to using brownfield land which has had previous use.

In software engineering jargon, a greenfield is a project which lacks any constraints imposed by prior work. The image is that of construction on greenfield land, where there is no need to remodel or demolish an existing structure. Such projects are often coveted by software engineers for this reason, but in practice, they can be quite rare.

see World Bank Glossary page

Greenfield Projects. A private entity or a public-private joint venture builds and operates a new facility for the period specified in the project contract. The facility may return to the public sector at the end of the concession period....