Retained earnings
Profit a corporation keeps instead of paying out to shareholders, which a C corp can hold after paying its 21% tax.
Retained earnings are the after-tax profits a corporation has kept rather than paid out as dividends. For a C corp, keeping profit is what makes the structure worth it: the profit has paid the 21% corporate rate under Section 11, and no second tax is due until it is paid out.
That can make a C corp cheaper than a pass-through for an owner who reinvests most profit and whose personal rate would be higher than 21%. The dividend tax is deferred, not cancelled.
There is a limit. Section 531 charges a 20% accumulated earnings tax on profit kept beyond the reasonable needs of the business. Section 535(c) gives a credit so the first $250,000 of accumulated earnings is generally safe, or $150,000 for service corporations in fields like health, law, accounting and consulting. Above that, the company should be able to show what the money is for.
In a pass-through business, profit is taxed to the owners every year whether kept or not.