Financial independence is when you have enough money to sustain
your desired lifestyle and have the time to do as you like. For
example, you can take a holiday for 6 months without having to
worry about not having income.
Let me give you an example. A doctor may earn high income but he
trade it with his time. If he stops working, he will not have
income.
Alternatively, he owns a clinic (or a chain of clinics) which he
hire other doctors to run. In this case, he does not need to work
at his clinic and still have income - also known as passive
income.
Of course, to achieve that, he would have thought harder and put in
the effort to build up his business.
Note that financial independence might not be necessary be that you
drive a ferrari and live in a big house - unless that's your
desired lifestyle.
You can also be financial independent if you live in a HDB flat,
drive a normal car (or don't drive a car), have income to sustain
your simple lifestyle, and you can choose to work for fun 
People like Bill Gates and Donald Trump, they work because they
want to, not because they need to.
