There are 2000 points available and distributed over the players from the start and the objective is get a certain amount of them; e.g. 1000 of these points as a solo player. The score you have displays a contrast between your provinces, the morale of those provinces, the upgrades that have been built there and all the provinces you do not have, their morale and available upgrades.The most dominant of the factors mentioned are the provinces you have and the morale each one of them has in relation to all the other provinces on the map and their particular morale. It is therefore an economic score (that can be considered to quantify military potency).
Some reservations have to made in asserting that the score does reflect economic power however: the DE score makes no distinction between single resource provinces and double resource provinces, while the latter are economically very potent since they give double the resource output for only a single province upkeep cost; making them more than twice as valuable as single resource provinces.There is a bonus to 99+ morale provinces, but this extra score, giving a considerable extra 27% points to a 100% morale province, reflects no real economic power and are in that sense empty points that can distort the view on how economic power is actually distributed in the map.