In networking, a greenfield deployment is the installation and configuration of a network where none existed before, for example in a new office. A brownfield deployment, in contrast, is an upgrade or addition to an existing network and uses some legacy components. The terms come from the building industry, where undeveloped land (and especially unpolluted land) is described as greenfield and previously developed (often polluted and abandoned) land is described as brownfield.
Greenfield는 새로 구축하려고 하는 네트워크
Brownfield : 기존에 설치된 네트워크
참조 : http://searchunifiedcommunications.techtarget.com/definition/greenfield-deployment