Extortion is getting money out of people by making threats; however, one point of extortion is that those making the threat have no authority to do so.
So if a parent tells his own child that if she doesn’t stop whining about wanting him to buy her candy at the store she will get no dessert, that is not extortion, because the father has authority over the child. The father’s acts are bound by morality–his authority is not unlimited, but when he crosses the line it is not called extortion but abuse.
In the same way, the police do similar things–pay this ticket or loose your license, come out of the car with your hands up or we’ll arrest you–but they too have the authority to do that.
Now, if some guys with bad accents come into your shop and let you know it will be busted up if you don’t pay them “protection,” that’s extortion.