What are 13f securities?
13f securities are the securities that hedge funds have to report ownership of in their 13f filings.
Institutional investors do not have to report ownership of every stock in their portfolio, they only have to report stocks that are designated as 13f securities by the SEC.
Every quarter the SEC publishes an official list of securities and requires large institutions are to declare ownership in any of those stocks, options, etc. Those securities are called 13f securities, and the reports filed by the institutions are called 13f filings.