Cash flow
The net cash generated or consumed by a company over a period. Free cash flow deducts capital expenditure from operating cash. It is the most direct measure of value creation: a profitable company without cash can still fail.
In practice
The cash flow statement is the hardest financial statement to manipulate — unlike the income statement, which can be inflated by aggressive accounting policies. An experienced investor routinely compares net income and operating cash flow: a persistent gap (rising income, falling cash) signals either deteriorating working capital or accounting anomalies. For a startup, burn rate and runway are the primary survival metrics.