云泥之别

yún ní zhī bié

(idiom) a world of difference

云

yún

abbr. for Yunnan Province 雲南省|云南省[Yun2 nan2 Sheng3]

泥

ní

mud

之

zhī

(possessive particle, literary equivalent of 的[de5])

别

bié

to leave; to part (from)