13D filing (>5% ownership)

A 13D filing is a public disclosure that someone has bought more than 5% of a company's stock. When an investor crosses this ownership threshold, the SEC (Securities and Exchange Commission—the government agency that oversees stock markets) requires them to file a 13D form within 10 days, revealing who they are, how much they own, and what they plan to do with it. You'll encounter these filings when activist investors or major players are making significant moves in a company. It matters because it signals potential shake-ups: the new owner might push for management changes, influence strategy, or attempt a takeover. For example, if an investment firm disclosed a 13D filing showing they'd acquired 6% of TechCorp Inc., it could spark speculation about their intentions.