An alienable right is one which can be assigned to another.

Your physical, real (land), and usefruct rights (as with intellectual property rights) can be alienated in the sense that you can be deprived of them and then they can be assigned to another entity.

Inalienable rights can be denied to you, but cannot be made alien in the sense that another receives their benefits. Your own life, your own happiness, your own liberty, among other privileges you may enjoy, can be deprived of you. But nobody else can receive their benefits.

The notion of inalienable rights is not absolutely fixed. In 1800, you would have had an inalienable right to the function of your own heart, lungs, kidneys, liver, etc. With organ transplants, these are now alienable rights, as those organs (and others) can be removed and given to others, through advances in medical technology.

That is, the benefits or possession of property can be transferred to another. The ability to benefit or possess cannot. Those last can be denied, and the objects of them transferred, but the right to enjoy, much as happiness or enjoyment itself, is inalienable.

> Obviously the US govt takes away its citizens' rights

There is a system of laws enacted by representatives of the people and proven out in courts, for example Eminent Domain.

To your point, that "nation of laws" concept is tending toward more of a theoretical than practical thing.