Well, I'm not sure there's any definition that's going to come straight from first principles, but I see a wealth tax as something closer to the way we tax corp

Well, I'm not sure there's any definition that's going to come straight from first principles, but I see a wealth tax as something closer to the way we tax corporations, which is to tax "profit" not "revenue". A personal income tax is more of a revenue tax - even if someone has to spend every dollar they make on kids, health care, rent, etc - we still tax it. We try to fix this a little, by offering deductions that we think make sense. But a wealth tax seems like a more direct way to get at this idea. Levy a tax on the money that people are able to accumulate, not on the money that flows through them.