People who have been involved in project implementation may know what "Greenfield" and "Brownfield" projects mean.
Prior to being employed by EPCM companies, I never knew what these terms mean. Being a farm kid, the greenfield I knew was totally different from the greenfield I currently know.
In project terms, the meaning of these terms are
Greenfield Project - A project development which is totally new not associated with any existing infrastructure.
Brownfield Project - A project which is an expansion or retrofit of an existing infrastructure to improve functionality.
Update:
In the current project that I working with, it is truly annoying for people who has years of experience working in the Oil & Gas industry but still doesn't know the difference between greenfield and brownfield projects.