手のひら

掌 or 手の平
te no hira
One's palm

Here is the first line of the direction I saw on the back of my 化粧水 (けしょうすい - facial lotion)

洗顔のあと、手のひらまたはコットンに500円硬貨大をとり、顔全体になじませます。
Sengan no ato, te no hira mata wa kotton ni gohyaku en kouka dai o tori, ganzentai ni najimasemasu.

If you know Chinese...you can pretty much guess what it's saying...
After you wash your face, in your hand or cotton, 500 yen coin size, "doing something" to the entire face. :-)