A handprint is the print of the palm of a hand. For example if paint is applied to the palm, and the hand is then pressed against a surface, a print of the hand will show.
A good spank on an unmarked and un-reddened bare bottom will also leave a red-pinkish handprint (also known as hand-mark, see the images on the right and below).
Spanking cartoon of the young Sammy Simpkins (F/f) by Dave Ell.
Drawing of a nude man with a handprint on his butt cheek.
Drawing from the visual novel Tricolor Angels.
A handprint on a bottom.