JohnS47:
Spanking can only be performed on the buttocks. Striking any other part of the body makes it something else.
This sounds a little prescriptive, John. I'm rather dubious of anyone trying to define what is, or isn't, 'real spanking'. As a lifelong kinkster, I try to be tolerant of other people's kinks, or of variants of my own, even if I don't happen to share them.
My dictionary defines 'spank' as 'to slap or smack with the open hand, esp. on the buttocks'. Especially, but not exclusively. Quite a lot of girls, I've found, enjoy being spanked on the thighs, on the breasts, or (in particular) on the pussy. I'd never spank a girl's breasts as hard as I'd spank her bottom, but a flurry of fast light spanks on the breasts can be quite a turn-on for her, as can tweaking or nibbling her nipples. Of course you, or she, may find the idea a turn-off; but practiced subtly you might find it can add considerably to the fun.