[Dwolb]

That's the investopedia definition.

Here's an alternate definition (and you'd adjust based on a given industry or company)

Start with Net income + expenses not using cash (such as depreciation and amortization) - revenues not providing cash (such as recognition of deferred revenues) - increase in working capital or + decrease in working capital - increase in required cash balances or + decrease in required cash balances + interest paid in cash (recall that all firms must disclose this number) - interest tax shield (the tax “savings” from financing charges due to the tax deductibility of interest) - long term capital investment (including, but not limited to capital expenditures or “CAPEX”) + cash from sales of assets (including sales of PPE)

= Free Cash Flows to the Unlevered Firm

You'd continue on with more calculations to get to free cash flows to common equity or whatever you're interested in.