A form the Canada Revenue Agency requires Canadian residents to file if the total cost of specified foreign property they hold exceeds $100,000 CAD at any point in the year, typically in a non-registered account.
Once your foreign holdings — things like US-listed stocks, foreign bank accounts, or foreign rental property — add up past $100,000 CAD in cost (not just value), the CRA wants a report disclosing what you own and where. It's a disclosure requirement, not a tax in itself, but missing it carries real penalties.
Canadian-listed ETFs that happen to hold foreign stocks (like a Canadian S&P 500 ETF) generally do not count toward the threshold, since legally you're holding a Canadian security — even though the underlying companies are foreign. Holdings inside RRSPs and TFSAs are also excluded. It's specifically about directly-held foreign property in non-registered accounts.