If you look at the hints and tips for the "Work" skill, it explains it there. This is the relevant paragraph.
"Crofting is a traditional form of land tenure found in the Scottish Highlands and Islands. Often, small parcels of "better" are worked by individuals and families, while a larger area of poorer land is used commonly for grazing animals. A croft is a croit and a crofter is a croitear."
It's common to hear a croft defined as "a small parcel of land surrounded by legislation."