The number of video outputs refers to the number of physical video connectors (HDMI, DisplayPort, DVI, VGA, USB-C Alt-Mode...) present on the graphics card. The parameter refers to hardware ports only and does not say anything about how many monitors can be run simultaneously; the two quantities may differ (e.g. a card with two DisplayPorts and one HDMI can support up to four monitors thanks to the MST hub).
