":I've reworded the lead to try and reduce the ambiguity in the definition.  Hopefully this helps.  The common definition of a flat tax (which is mostly used to imply income taxation as oppose to consumption or a sales tax) is usuall not a horizontal line in regard to average tax rate and progressivity.  Certainly the term of flat tax implies one rate but in practice and legislation, it may be one rate 35% but exempts income up to a certain level - so they don't count 0%.  This is of course regarding a marginal tax rate view and when such an exemption is applied to an average tax rate it becomes a progressive tax.   (talk) 0:57, 25 June 2007 (UTC)

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