Specifically, double-taxation is when you pay taxes twice on the SAME earnings. Take the example of a US citizen living abroad in a country with lower income taxes. They will have to pay foreign as well as US income taxes: two like, you point out, rather than one. But the IRS agrees that double-taxation is mean, so they give you a foreign tax credit for the tax you've already paid. You pay an amount to the IRS to make up the difference in income tax. If it were double-taxation you would have to pay the full US income tax on the money you earned, after already having paid the full foreign income tax on it as well.
(Note I've been talking about plain-vanilla income, it's a whole new ball-game if you think about other investment income.)
Double taxation is the levying of tax by two or more jurisdictions on the same declared income (in the case of income taxes), asset (in the case of capital taxes), or financial transaction (in the case of sales taxes).
Specifically, double-taxation is when you pay taxes twice on the SAME earnings. Take the example of a US citizen living abroad in a country with lower income taxes. They will have to pay foreign as well as US income taxes: two like, you point out, rather than one. But the IRS agrees that double-taxation is mean, so they give you a foreign tax credit for the tax you've already paid. You pay an amount to the IRS to make up the difference in income tax. If it were double-taxation you would have to pay the full US income tax on the money you earned, after already having paid the full foreign income tax on it as well.
(Note I've been talking about plain-vanilla income, it's a whole new ball-game if you think about other investment income.)