Tax deducted by a foreign government on dividend or interest income paid to a non-resident investor, subtracted automatically before the payment ever reaches the investor — commonly 15% on US dividends paid to Canadian residents, under the Canada-US tax treaty.
If you own US stocks and they pay a dividend, the US government takes a cut before that money crosses the border to you — you never see the full amount in the first place. It's automatic and invisible in your account statement, which is exactly why it's easy to overlook.
Thanks to the Canada-US tax treaty, this 15% withholding tax is waived specifically when a Canadian resident holds US-listed securities directly inside an RRSP. That exemption does not extend to Canadian-listed ETFs that hold US stocks (like VFV) — the tax still applies at the fund level in that case, regardless of which account holds the Canadian ETF.