|Kanji in this term|
億 ("one hundred million") + マンション ("apartment"), based on a pun on マン, which can mean "ten thousand". Ordinary apartments have rents in the order of tens of thousands of yen, but a luxury apartment may have much higher rents, so the "ten thousand" is replaced with "one hundred million" since only someone with hundreds of millions of yen could afford one.
億ション (hiragana おくしょん, romaji okushon)
- luxury apartment