Cash flow
Etymology
"Cash" comes from Middle French "caisse" (money box), from Latin "capsa" (box) — the word first meant the box itself, then the money kept in it. "Flow" adds the sense of movement in and out. Together they name money in motion, as opposed to wealth sitting still.
noun phrase · /KASH FLOH/
The actual movement of money into and out of a person or business over time.
What it names
The timing of money, not the total of it — whether cash is on hand when bills come due, which is what actually sinks households and firms.
Example
The business was profitable on paper but nearly folded from cash-flow problems when clients paid late.
Related idea
Distinguish profit: profit can be earned the moment you make a sale, but cash flow depends on when you are actually paid — a profitable company can still run out of cash, and a struggling one can survive on strong cash flow.