Fields:Fields represent the amount of productive agricultural land. Some areas had more than they needed, others had to import (usually via ship, their being no efficient land transport).
Industry:This is an indication of the industrialization and manufacturing in the fief. The most common items were metal working, mining, cloth weaving, ship building, weapons manufacturing and manufacturing in general. Although most fiefs were self sufficient for most essential manufactured goods (blacksmith, harness maker, etc.) there was a growing amount of centralized and specialized industrial activity. After all, this was the beginning of the Renaissance, which laid the ground work for the Industrial Revolution four centuries hence.
Weather:Weather changes, if this value is less than one, GDP and population will suffer, if greater than 1, these will benefit.
Treasury Balance:This is the amount of money in the treasury of that fief. If the fief is conquered, it's treasury goes to the new owner.