A banknote with a face value of 10,000 yen (the 10,000-yen bill). Often called "ichiman-en satsu" in everyday speech.
財布に１万円券が一枚だけ入っていた。
There was only one 10,000-yen bill in my wallet.
店員が大きい額の支払いだったので、１万円券を確認した。
Because it was a large payment, the clerk checked the 10,000-yen bill.
ATMでは硬貨は出せないが、１万円券や千円札は使える。
ATMs don't dispense coins, but they can handle 10,000-yen bills and 1,000-yen notes.