Not sure why you were downvoted for what seems like an honest question.
Stable coins and other tokens which are not native blockchain assets are referred to as cryptocurrencies (shiba inu is one such example of this which is not a stablecoin).
Cryptocurrencies like Bitcoin, Ethereum, Solana, Avalanche, and a bunch more are also the native token of their blockchain. In other words, they're the primary mechanism for rewarding participants in the blockchain at the node/consensus level for their efforts, and they're also the currency used for getting transactions included into blocks on their blockchains (for paying the transaction fee, also called "gas" on many chains).
Blockchains which have the capability of running user-submitted code are said to have "smart contracts", bits of code which execute when certain conditions are met during a transaction. Most chains with smart contract functionality also include standards for deploying what are referred to as "tokens" which are essentially smart contracts which provide a conforming interface for interacting with the token and tracking the balances of users on that blockchain.
While all tokens provide the same basic interface, they can also have custom code which affects the behaviour. In the case of most stablecoins (the centralized ones), that means privileged parties who can do things like mint new tokens, or blocklist addresses from being able to transact those tokens.
USDC for example, operates by allowing users to create an account with the issuer (Circle), deposit USD, and then have Circle "mint" new USDC tokens to your address. They also let users go the other way and redeem their USDC. However, not everyone who wants to hold USDC needs to mint it; they can also buy it on a centralized or decentralized exchange (decentralized exchanges also being governed by specialized smart contracts of various types).
There are also "algorithmic stablecoins" which, in theory, don't have privileged issuers, and use various protocols to attempt to "peg" the price to the price of some stable asset / USD (these are complicated, have many different methods of operation, and are not really proven to be completely resilient at this point). UST/LUNA was the big one that exploded about a year ago, vaporizing several billion dollars over the course of a few days.
So, "stablecoins" are a cryptocurrency, but not a native blockchain asset (unless there's a chain that primarily accounts in a stablecoin which I'm not aware of), and the primary stablecoins people hear about are also not decentralized.
Stable coins and other tokens which are not native blockchain assets are referred to as cryptocurrencies (shiba inu is one such example of this which is not a stablecoin).
Cryptocurrencies like Bitcoin, Ethereum, Solana, Avalanche, and a bunch more are also the native token of their blockchain. In other words, they're the primary mechanism for rewarding participants in the blockchain at the node/consensus level for their efforts, and they're also the currency used for getting transactions included into blocks on their blockchains (for paying the transaction fee, also called "gas" on many chains).
Blockchains which have the capability of running user-submitted code are said to have "smart contracts", bits of code which execute when certain conditions are met during a transaction. Most chains with smart contract functionality also include standards for deploying what are referred to as "tokens" which are essentially smart contracts which provide a conforming interface for interacting with the token and tracking the balances of users on that blockchain.
While all tokens provide the same basic interface, they can also have custom code which affects the behaviour. In the case of most stablecoins (the centralized ones), that means privileged parties who can do things like mint new tokens, or blocklist addresses from being able to transact those tokens.
USDC for example, operates by allowing users to create an account with the issuer (Circle), deposit USD, and then have Circle "mint" new USDC tokens to your address. They also let users go the other way and redeem their USDC. However, not everyone who wants to hold USDC needs to mint it; they can also buy it on a centralized or decentralized exchange (decentralized exchanges also being governed by specialized smart contracts of various types).
There are also "algorithmic stablecoins" which, in theory, don't have privileged issuers, and use various protocols to attempt to "peg" the price to the price of some stable asset / USD (these are complicated, have many different methods of operation, and are not really proven to be completely resilient at this point). UST/LUNA was the big one that exploded about a year ago, vaporizing several billion dollars over the course of a few days.
So, "stablecoins" are a cryptocurrency, but not a native blockchain asset (unless there's a chain that primarily accounts in a stablecoin which I'm not aware of), and the primary stablecoins people hear about are also not decentralized.