A currency is a system of money in general use in a particular country. For example fiat. Fiat money gives central banks greater control over the economy because they can control how much money is printed. This is how the state works.
Naming them "coins" isn't false, they can be considered as "coins" (Hence "altcoins"). In ancient times, people used to exchange goods with gold coins and there were times when they passed over their national currency with those coins. And that's because they were broadly accepted by anyone, since they were made out of gold.
I just wanted to state that I find it falsely to use the term "currency" over something that can be used by anyone in the world and it is definitely not determined or even acceptable by a nation.
I think that this should be a correct sub-board for this thread.
Put exact, technical and mathematical mind into crypto market and he start to create fascinating things. He will become rich. He will start to change word.
Put humanistic mind into crypto market and he will waste time on nomenclature. Who cares man
"A currency[a] in the most specific sense is money in any form when in use or circulation as a medium of exchange,"
https://en.wikipedia.org/wiki/Currency
You can use bitcoin as well as majority of altcoins as medium of exchange so ... they are currencies. They are not currencies if you monopolize this word such as governments did. We are here to be able to use a medium of exchange that is not inflated and restricted by single entity. For us, crypto believers/enthusiasts, bitcoin is more a currency than fiats are.