CEO means Chief Executive Officer.
The Chief Executive Officer is the boss of the company. The Sarbanes-Oxley Act made the chief executive officer of a publicly held company criminally responsible for the financial statements issued by the company. This means that not only the Chief Financial Officer, but also the Chief Executive Officer must sign the statements. If they are found to be intentionally fraudulent, the Chief Executive Officer might be sent to prison. The intent is to make sure that ordinary investors don’t lose money on the stock market because of a fraud perpetrated by the officers of a company.