So let's figure it out. Let's start with what everyone understood right away:
Bitcoin is a good topic for discussion, although a separate and rather large one, so briefly:
Yes, this is the same Bitcoin, everyone knows it, everyone has seen it. Let's limit ourselves to this. (At least for now...)
Altcoins are also a broad topic, but let's start little by little: These are alternative coins to Bitcoin.
Yes, that's all the explanation.
Literally everything that is not bitcoin (though not stablecoin or fiat) is an altcoin.
Altcoins, in turn, are divided into a huge number of sectors: AI, shitcoins, memecoins, infrastructure, DeFi...
As I said - the topic is not small, you can study it yourself at your leisure (or for the lazy wait a little, we will consider this point soon)
Fiat - well, surprisingly everything is simple here.
Fiat currency is the currency of the state, dollars, euros, rubles, hryvnias, and everything else...
Their main difference from cryptocurrencies is that they are issued and controlled by the central banks of states. The value of fiat money is supported by the trust in governments and the economic stability of the countries that issue them.
They are not decentralized and their volume can be increased or decreased depending on policy.
And now stablecoins:
This is where it gets interesting, this is a cryptocurrency based on 'stable' (as far as they can be) assets. For example, on dollars.
Let's take an example: $USDC USDT is a cryptocurrency pegged to the dollar in a 1:1 ratio
It is worth noting separately the very fact of the existence of several stablecoins, for example USDC and USDT. What is the difference between them?
Different companies are responsible for them (which leads to different behavior)
USDT (USD Tether): Operated by Tether Limited, a subsidiary of iFinex, the same company that owns the Bitfinex crypto exchange, Tether was launched in 2014 and is considered one of the first stablecoins.
USDC (USD Coin): Operated by Circle in partnership with Coinbase. The technology platform and standards for USDC are maintained by the Centre consortium, which brings together participants to maintain the sustainability of the stablecoin.
Apart from these, there are a few more worth mentioning:
$FDUSD (First Digital USD) is a stablecoin launched by First Digital Group. It is also pegged to the dollar 1:1. There is not much to add about it
UST (Terra USD) is a stablecoin that was part of the Terra ecosystem and pegged to the US dollar. However, unlike the others, UST was not directly backed by fiat reserves. Instead, its rate was maintained through an algorithmic peg to the LUNA cryptocurrency (Terra's token).
(But the key word is 'was': The algorithmic model couldn't handle the huge swings in the market. As a result of the mass exodus of users from UST, its peg to the dollar was broken, and the price fell well below $1. This caused panic selling and a collapse of the Terra ecosystem, including the LUNA token, which lost almost all of its value.)
In fact, what it was, how it worked and why it fell apart is also not a small topic, but I would not call it interesting. If you want, I can consider this question, but is it worth the time spent?
Clarification: The information presented here does not claim to be reliable, always check the information received yourself (and do not hesitate to ask questions or correct the author if necessary).