what are the characteristics of a tax?

1) Nobody wants to pay it
2) You don't (legally) have a choice
3) Whatever it is, it's too much

Not trying to be funny, but all of the above is true.

It is normally extracted at 'vulnerable' points - eg: 'bottle necks'
- import taxes
- taxes on wages extracted from paypacket
- death duties
- sales tax (retailer is monitered)
- property sales/purchase tax

It is also raised on things that people /want/ to buy
- tobacco, alcohol, petrol (gas)

Also taxes tend to multiply - they are seldom abolished

The main characteristic of a tax is that it is not voluntary, it is a
firm conditional upon an action or event:

If you make X amount of money Then you pay X amount of income tax.
If you buy cigarettes Then you pay X tax for each box {or carton or cigarette}.
If you import goods Then you pay X% tax on their value.
If you inherit X amount of money Then you pay X amount of inheritance tax.
...

There could be thousands of examples of taxes, however the common
theme is that it is conditional upon an event or action... and if that
event or action occurs then you pay the tax.  Tax is never voluntary
given the condition, however many entities who impose taxes allow for
"deductions" or "credits" that allow you to reduce the taxes you pay
if you meet other conditions.

Some examples of these in the US are:
IRA contributions
Charitable donations
Business expenses
Interest payments on your residence