13D filing (>5% ownership)

A 13D filing is a public document that someone must submit to the SEC when they buy more than 5% of a company's stock. Think of it as a transparency rule—once you own that much, the market needs to know about it. You'll encounter these filings when tracking major investors or potential takeovers, since big ownership stakes can signal serious intentions. The filing includes who the buyer is, how much they paid, and what they plan to do with their stake. For example, if an investment firm quietly accumulated 6% of TechCorp shares, they'd have to file a 13D disclosing their position and whether they're planning to push for board changes or just holding long-term. It's basically the SEC's way of keeping things honest.