Basically, in our society, smaller is considered to be better where noses are concerned. This trope is an aversion to that; someone is considered attractive because of their big nose. Named for a term which actually doesn't mean this, but is often used as a more flattering way of calling a nose big. Although women are hit with the whole "smaller is better" thing more, this trope isn't exclusive to one gender. I can't think of any examples, but I know I've seen it.
Hello, Unknown Troper. You'll need to get known to lend a hand here.