Hi,
It depends. Based on how the "Detailed tax display" setting is configured in your HikaShop configuration, this word either comes from:
- the namekey of your tax rate you can edit via the "manage tax rates" button of the the System>Taxes menu. In that case, you would have to create a new tax rate with the name you want and edit your tax rules to associate them with the new tax rate.
- a translation key that you can override like this:
www.hikashop.com/download/languages.html#modify