Cash flow
The money coming in minus the money going out over a period, usually a month. Positive cash flow means you spent less than you earned.
Your monthly cash flow is take-home pay and other income minus everything you spend. Positive cash flow is what funds savings and extra debt payments.
Negative cash flow means the gap is being covered by savings or debt. Tracking your spending for a month shows where the money goes, so you can close the gap. Small changes on both sides add up.
Example
Take-home pay of $3,800 − spending of $3,500 = $300 of positive cash flow for the month.