In looking at the names of URW's fonts, I see they follow a naming standard, but I was stuck in trying to decipher all the versions.
The typical letters are D, P, L, and E.
I think D is Display, with tighter character and word spacing. P seems to be Poster, with even tighter spacing and a lighter weight in the characters. L, according to some Google searching, is Laser — width compatible with built-in Postscript fonts for use back in the bad old days. I have no idea what E is, however.
Can anyone shed any light onto this?