In economic strategy board games, it’s very common to have an arc of growth over the course of the game. You start out with few resources, and then you invest those resources to bolster your income, which then gets reinvested to grow even more, following an exponential trajectory. Central to this growth trajectory is the concept of capital.
In economics, capital is understood as durable goods that are used to increase or enable production. The classic example of capital is factory machines, but capital could also be something abstract, such as an education. People commonly understand capital as simply money, which is true insofar as money is commonly invested into capital. And so it is in economic board games, where you invest fictional money into fictional capital in order to increase fictional production.