Many games, contain aspects which gamers call "the economy". For example, there might be goods such as gold, lumber, magical gems, and they might be exchangeable for each other (often with some loss), and also exchangeable for other things, such as mines or workers, which can be used to obtain more goods.
Economics, the academic discipline, sometimes starts with the idea of voluntary pairwise exchange. This is actually very rarely part of the economy within games. Let's imagine an academic discipline called "command economics", which focuses exclusively on those economic questions which remain, even if there is no such thing as voluntary pairwise exchange.
As far as I can tell, there are two ways that generic game mechanics get characterized as economics. The first is via exchange. For example, if a blood mage can cast a generic heal spell that costs mana and results in increased hp, and also cast a blood magic spell that costs hp and results in increased mana, then there mana and hp are exchangeable, similar to two currencies in a foreign exchange market. Almost any state change can be framed as an exchange - sailing from city A to city B in "Patrician" is giving up immediate access to the city A in exchange for immediate access to city B. Switching from stance to stance in "Soul Calibur" or "Street Fighter" can be characterized as an analogous exchange.
I think this first analogy is too facile, and can be stretched too far. If motion and state machines are command economics, then what isn't command economics?
The second way that generic game mechanics get characterized as economics is via investment. An example of investment would be if you have a gold mine, and the gold mine produces a regular sequence of payments of gold, and you have the option to purchase another worker using gold, and the worker, assigned to the mine, will raise the rate or size of the payments of gold, then you have to choose between gold now and gold-income later. If you reinvest a constant fraction of your gold-income in workers, then your gold-income and the number of your workers will rise exponentially.
One way to characterize investment is an "over unity engine". A facility and/or process that moves or exchanges goods in such a way as to turn N goods into N * (1 + epsilon) goods. Command economics, as I am using the term, studies over unity engines.
Over unity engines are sortof common, and also sortof rare. Generally, what happens is that at some level of analysis or according to some model, an over unity engine exists. However, if you take that model (a simplified, even more artificial model of the already simple and artificial game), and try to follow the exponential path in the actual game, you almost always find that you are at some scale blocked by an aspect of the actual game which was neglected in the model.
For example, it may be the case that after adding more and more mining workers, the flow of workers back and forth between the mine and your home base becomes congested. Or as you cut more and more lumber from a forest, the edge of the forest, which had seemed inexhaustible, starts retreating further from your base, forcing your lumberers to spend more and more time walking to the forest and carrying lumber back from the forest, time which was neglected in the model.
After incorporating the new bottleneck into your model, it is entirely likely that the new, more elaborate model still contains one or more over-unity engines, probably with lower asymptotic growth rates. Follow the exponential growth curve long enough in the new model, and you will likely find another bottleneck.
This is command economics: over-unity engines and where to find them, model/reality gaps and what they look like (what they feel like when you run into them), organizing bottlenecks into sequences, taxonomies, or networks.