Slang for the 10,000-yen banknote, named after Yukichi Fukuzawa whose portrait is on the bill.
財布に諭吉が一枚しか入っていなかった。
There was only one 10,000-yen note in my wallet.
新しいスマホは諭吉が何枚も飛ぶね。
The new smartphone will cost several 10,000-yen notes.
飲み会で彼が諭吉を出して割り勘してくれた。
At the drinking party he paid with a 10,000-yen note to split the bill.