One of the things that many investors look for in a company is high insider ownership. This seems to indicate that insiders, those who probably know the company best, are confident of its future success. While not a perfect indicator, it often is a characteristic of stocks that become 100-baggers or better.
The flip side of this is that companies where the insiders own less than 10% of the common stock are liable to be poor long-term investments, though profitable short term trades are not impossible.
This is the practice of buying or selling shares of a company's stock (or some other security) based on knowledge that was acquired as an officer of the company, and that is not available to the general public. This is illegal.