Form 3

A document that must be filed with the Securities and Exchange Commission (SEC) by an insider affiliated with a public company's operation or by any investor owning 10% or more of the company's outstanding shares.

Investopedia Says:
This document must be filed with the SEC no later than 10 days after an insider becomes affiliated with a company, and it must be filed for each company in which a person is an insider, regardless of whether or not the insider has an equity position in the company at that time.

Related Links:
Find out how this regulatory body protects the rights of investors. Policing The Securities Market: An Overview Of The SEC
These transactions reveal much about a stock. We go over what to consider and where to find it. Keeping An Eye On The Activities Of Insiders And Institutions
Some insider trading is actually legal - and can be extremely telling for investors. Uncovering Insider Trading

Form filed with the Securities and Exchange Commission and the pertinent stock exchange by all holders of 10% or more of the stock of a company registered with the SEC and by all directors and officers, even if no shares are owned. Form 3 details the number of shares owned as well as the number of warrants, rights, convertible bonds, and options to purchase common stock. Individuals required to file Form 3 are considered insiders, and they are required to update their information whenever changes occur. Such changes are reported on Form 4.