[Tagging] What exactly is a greenfield?

[Nathan Edgars II]

According to the wiki, landuse=greenfield "Describes land scheduled
for new development where there have been no buildings before". Does
this mean that any undeveloped land owned by a developer or zoned as
planned development is a greenfield? If so, should a bug be filed on
trac to render it less obtrusively than the construction/brownfield
brown?

Also, what if land with another landuse like farm is scheduled for new
development?