Value Added Tax, or Sales Tax as some places call it.
I notice on my print books (looking at my Spotlight set as England) it gives the price and then (excl. VAT). No VAT is charged on printed books in the UK ( and many other countries also) and (excl. Vat) is only noted on prices when VAT will be added at the checkout. (20% in the UK) but as there's no VAT added to printed books then it should not suggest that it is. Why does it say (excl. VAT) then? It does not say it on Amazon, for example.
It is added to digital books now, but on Amazon it still does not say (excl. VAT) because no doubt it's already been added and that's the price you see.