cash cow

profitable enterprise, business that earns a lot of money

In business, a cash cow is a product or a business unit that generates unusually high profit margins: so high that it is responsible for a large amount of a company's operating profit. This profit far exceeds the amount necessary to maintain the cash cow business, and the excess is used by the business for other purposes.
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Noun
1. a project that generates a continuous flow of money
(synonym) moneymaker, money-spinner
(hypernym) project, projection

A company that pays out most of its earnings per share to stockholders as dividends. Or, a company or division of a company that generates a steady and significant amount of free cash flow .