back of the hand
Refers to the outer surface of the hand, opposite the palm. Used in everyday contexts.
Don't forget to put sunscreen on the back of your hands.
He wiped the sweat with the back of his hand.
手のひら is the flat inner surface of the hand, while 手の甲 is the outer, knuckle side.
Compound of 手 (hand) + の (possessive particle) + 甲 (outer surface, shell). The reading こう for 甲 is standard in this anatomical term.