ERC

• Token standard used by Ethereum
• "ERC-20 came about as an attempt to provide a common set of features and interfaces for token contracts in Ethereum, and has proved to be very successful. ERC-20 has many benefits, including allowing wallets to provide token balances for hundreds of different tokens and creating a means for exchanges to list more tokens by providing nothing more than the address of the token’s contract. The benefits of creating a token as ERC-20 compliant is such that very few token contracts today are created any other way (8-2018) new ERC standards are being made however."
• Other well known ERC's are ERC223, ERC777, ERC-1155 and ERC-721o
• From a blog by Polygon (17-7-2023):

"Due to Ethereum’s permissionless nature and ability to execute arbitrary smart contracts, anyone can create assets on Ethereum. Those assets, however, are stored in smart contracts, not the owner’s accounts.

For example, an ERC20 token is represented by a contract. This contract is a simple registry that lists all the owners and their amounts in a global hashmap. The hashmap, in turn, tracks ownership. Transferring an ERC20 token, therefore, means changing the list of owners in that particular contract.

This model has tradeoffs. Transactions can only happen sequentially—there cannot be two different changes to that public list at the same time. And the list is public: Anyone can read the `balance_of` any other user.

Even the owner of an ERC20 token needs to look her balance up in those lists. This is why MetaMask doesn’t show all the tokens one possesses right away, but a user needs to add a token to get the balance. While ERC20 tokens are fungible, the model doesn’t change for non-fungible assets like NFTs using ERC-721."