Definition
The discipline of tracking money in (receipts) and money out (payments) over time to maintain solvency and fund growth. A common failure mode for small businesses even when they're profitable on paper.
Why it matters
Cash flow is what actually keeps the doors open, and a business can be profitable on paper yet still run out of money to make payroll or pay a supplier. The trouble usually comes from timing: money owed to you arrives later than the bills you have to pay now. Watching the timing of money in versus money out lets an owner see a squeeze coming and act on it before it becomes an emergency.