A PFIC is defined under U.S. tax rules. In this context, "Passive" means stocks and bonds are used to generate income and capital gains as opposed to operating an active business. PFIC rules are intended to prevent U.S. taxpayers from securing preferential tax treatment, such as tax deferral, from investing in foreign securities in comparison with U.S. domestic securities. "Passive" is not meant to reflect on the investment strategy of the ETF: both active and passive ETFs managed by Horizons ETFs can be "Passive" for this purpose.
For investors who file U.S. tax returns and want to avoid the negative consequences of owning a PFIC, Wealthsimple recommends you check the websites of the assets held in your portfolio to determine if PFIC annual information statements exist.
For example, Blackrock ETFs are PFICs, and the annual information statements are available here.