A more thorough explanation:

Regulation D is a rule made by the Securities and Exchange Commission (SEC) that controls certain types of private investments. Normally, when a company wants to sell securities (like stocks or bonds), they have to file a registration statement with the SEC. But Regulation D allows companies to sell securities without filing a registration statement, as long as they follow certain rules.

For example, under Rule 504 of Regulation D, a company can sell up to $5 million of securities to private investors without many restrictions. Under Rule 506, there is no limit on how much a company can sell, but they have to follow more rules.

Here's an example of how Regulation D might work in real life:

Let's say a small startup company wants to raise money to develop a new product. They don't want to go public and sell shares on a stock exchange, but they do want to sell shares to private investors. To do this, they decide to use Regulation D to make a private placement.

The company hires a lawyer to help them follow the rules of Regulation D. They decide to use Rule 506, which has no limit on how much they can sell. But they have to make sure that all the investors are "accredited investors" (meaning they have a lot of money or experience in investing) and they have to give them a lot of information about the company and the risks of investing.

The company successfully raises $10 million from private investors using Regulation D. They use the money to develop their new product and eventually sell it to a larger company for a profit.