Use Tax

See: User Fee.

The use tax is basically the same as a sales tax, but imposed by a government which, um...got grumpy that you went somewhere else to buy something.

You live in New York State, which has a 8.75% sales tax. You buy a set of steak knives online from Montana, which has no sales tax. You think you got a great deal, circumventing the whole sales tax thing using the magic of the Internet. But then New York sticks you with the use tax.

Since you're using the steak knives in New York and didn't buy them in New York, you still owe the tax. Basically, it acts as a catch-all in situations where the sales tax wasn't collected by the retailer, as typically happens with sales tax.