I would define it something like when a government entity forces you to pay more than you are paying right now.  They have gotten very crafty over time on how they extract money from us.  It gets difficult at times to calculate our overall tax burden.  You have the following, just off the top of my head:

Federal Income Tax

State Income Tax

Social Security Tax

Medicare Tax

Sales Tax

Taxes on utilities…phone, cable, gas, electric

Property Tax

And that’s just while you are alive, you may have to pay a tax when you die, too.

It is clear that politicians do not realize the burden us tax payers have.  Note ABC’s interview with the president (it gets interesting about 3 minutes into it).

http://www.youtube.com/watch?v=rL7ak__MGyw

I support the Fair Tax (www.fairtax.org).  It eliminates all income taxes and replaces it with a transparent tax.