Told ya! I think they're a tiny bit boomy now, but it's a bit hard to judge without a bass.
Anyway, yeah, a lopass filter is an EQ setting which you apply a certain frequency and dumps all the frequencies above that one you chose. It lets the frequencies below pass (hence its name lowpass). Most EQ plug-ins give you the option to apply a lopass filter, and to control at what frequency and how steep you want the cut.
For example, this is the post EQ I have on my guitars after POD Farm. Notice to the left there is a big slope cutting the super high frequencies. That's a LP, lopass, low pass or whatever you wanna call it.
I tend to apply both a lopass at 12KHz and a hipass (the opposite of a lopass) at 60Hz because you don't really need the information that's below and above those points for guitars. Whatever's in those kinds of frequencies is just eating up your mix's headroom and messing with the kick/bass and cymbals.