If you want to dive into that sort of thing i recomend looking into social constructivist theory, nuts to realise just how much of everything we live our lives by is really a product of people agreeing to do so rather than any struct objective measure.
Exactly, like crypto for example, it has no real world value (in fact it has negative real world value) and the only thing that makes it valuable is that enough people believe it has value.
It is neat seeing our agreement on these words change over time. And seeing a few people complaining about words not being used in its original meaning, thinking language is static. And cursewords going from taboo to common usage.
Did you know shark (most likely) comes from the dutch word schurk (meaning bad guy/villain/scoundrel)? Which is where Loan Shark comes from, not from the fish. And the fish was called Haye or Dogfish? At some point the english speaking people decided that the fish should be called "bad guys". Meanwhile, here in Norway we kept both the words "skurk" and "hai" from the dutch, in its original meaning.
I wish I found this so fascinating back when I was still in school and could have taken that path.
Depends on how we're framing it. We agreed on names of days and lengths of weeks based on our culture and tradition, but that's not really what today "is", though. What it "is" is the 171st rotation in the current revolution around the sun. No need to agree on anything there. That just is what it is.