Through any form of paid work. Selling stock etc. doesn't count, but returns from a business do.

Edit to add: if from a business, this will count profit, not revenue (so costs are subtracted).

Edit to add: Since this is going to come up, I'll clarify that business "profit" will be whatever I end up counting as profit on my 2023 taxes. This may be more complex than revenue minus costs, because of IRS rules about amortizing capital costs over multiple years. I'll just say that my current uncertainty about tax law will be built into the market 🤷‍