Cash flow means the inflows and outflows of your business. It is the difference between actual revenue (e.g. through sales) and expenses (bills, salaries, etc.).
In other words, cash flow represents your available funds. Cash flow is not the same as profit. Profit is the amount remaining after all costs for developing and delivering a product or service have been settled. Your cash flow is a good KPI for determining your financial position. Banks and other financiers will also study the development of your cash flow when you apply for financing or other services. So it's important to keep a close eye on your cash flow.