13F filing

A 13F filing is a quarterly report that large investment managers must submit to the SEC (Securities and Exchange Commission—the government agency that oversees stock markets) showing which stocks they own. Think of it as a public snapshot of a professional investor's portfolio. You'll encounter 13F filings when researching what big-name fund managers are buying and selling, which can give you clues about where smart money is flowing. It matters because these institutional investors often have teams of analysts, so their moves can be worth paying attention to. For example, if you notice that a famous hedge fund manager just bought a large stake in a company you're researching, that might be worth investigating further.