'In theory, and many times in practice, vineyards are designated "grand cru" (literally, "great growth") when they have shown the highest potential for greatness. It is emphatically not a classification of wine quality per se, but rather the potential of the site. An underachieving winemaker can easily make characterless wine from outstanding terroir, and a conscientious one can make a superior wine from a less-favored site. To help increase the quality of grand cru wines, they typically have the lowest maximum yields...' Source wikipedia.org
I heard this term being thrown around a lot and I thought it might be a good idea to explain it a bit. Grand Cru relates to terroir, so you might want to plow through the terroir article. If not, the simple of it is that the farm lots with the highest potential and best terroir can be considered Grand Cru. This applies to coffee most often when you see the term Grand Cru Kenya thrown around. You could however use the term to describe any agricultural site with great potential in wine, coffee, or even in teas.
The Cru classes have their roots when, in 1855 Emperor of France, Napoleon III ordered the chamber of commerce to set up a classification system for the most famous wine estates.
According to the 1855 Bourdeux classifications, below grand cru are premier cru, deuxièmes cru, troisièmes cru, quatrièmes crus, cinqièmes crus, and finally cru bourgeois.