Ripple
Ripple is a by product of converting AC to DC, and it's characterised by tiny voltage fluctuations that need to be suppressed in order to deliver clean power to your components.
As usual, there are standards for this kind of thing, with the ATX spec stating that ripple shouldn't exceed 120mV evaluated as a peak-to-peak value.
33.4mV doesn't look too hot when compared to the very best consumer supplies available, but remember, it's about one-quarter of the permissible limit. An easy pass for Rosewill in this instance.