system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What gives the USD value if it is no longer backed by gold?
gpt
Trust.  All forms of money are based on the trust that it will be valued when it is time to exchange it again.  Whether it is elements and minerals, like gold, or paper currency and coinage, when a person accepts it as compensation, they are trusting that when they go to give it as payment, it will be accepted.  Even gold only has value because we all trust that it does.  A person who accepts gold (or gold-backed currency) in payment, does so because they trust that when they try to give that gold to someone else, that person will accept the gold as valuable.

Currency is trusted because the government that created it says its good and will be acceptable.  That's one of the factors accounting for the fluctuations in currency exchange rates.  How confident are people that the government will continue to be able to back the money they issue.