I find the term "backed by" to be rather incoherent.

Does it mean to be redeemable for something, as old currencies were for gold?

Does it mean hard to produce, as we see with precious metals and real estate?

Does it mean value derived through threat of violence, as claimed by those who say the USD is "backed by the US military"?

Does it mean a combination of the above, or something else altogether?

It's one of those terms whose definition is so muddied and confused that I find it fruitless to engage with.