Effeminate underwear, briefs (usually) with no "Y-fronts", jocks, panties, knickers. Origin of word - Punjabi (India/Pakistan). Popularised in British English by usage in BBC comedy series "Goodness Gracious Me".
The noun "chuddies" is feminine. The masculine of it would be "chuddas".
One of those Def Leppard chaps wore Union Jack chuddies.