Capital takes different forms as it moves through this circuit: it can be money in the form of cash, bank balances, credit, etc. It can be commodities in the form of tools, factories, raw materials, consumer goods, etc. But money and commodities are only capital when they area part of this circuit. Money sitting in your pocket or factories sitting unused are not capital because they aren’t part of the circuit of capital. But they can become capital if they enter this circuit.
via What is Capital?.