palm of the hand
Refers specifically to the flat inner surface of the hand, similar to 手のひら but less common in everyday speech.
See also: 手のひら
手の腹で机を軽く叩いた。
I lightly tapped the desk with the palm of my hand.
Compound of 手 (hand) + の (possessive particle) + 腹 (belly), literally 'belly of the hand', referring to the fleshy inner surface.