From the FarmPlate glossary:

The term foodshed derives from watershed.  Just as watershed refers to an area where all waters flow in the same direction, a foodshed is an area that includes everything from the farm to where food is consumed or wasted.  Accordingly, foodsheds come in all shapes and sizes.  Today's food system is best described as a global foodshed, but foodsheds can be local or regional too.  These can be defined by a simple 100-mile radius or an entire valley, like the Hudson River Valley, and are particularly useful in promoting and describing local food systems.