It will ALWAYS refer to the polarity of the electrode: DCEP, DCEN. Direct current, electrode positive, Direct current Electrode negative. And REverse polarity is the same as DCEP, though, if you consult with Longevity, their manuals tell you erroneously otherwise.

But I imagine you know by now what straight polarity is.

Don't ever both with DCEN. No practical reason to do so. If you can't weld it with stick thin enough, go to TIG. DCEN isn't very practical, except for the thinnest of material. It'll make a mess usually.