ERC-20 (Ethereum Request for Comments) tokens are tokens that follow a set of standards defined for smart contracts on the Ethereum blockchain. ERC-20 defines the common rules for developers to adhere to when creating Ethereum tokens.
These standards enable smart contracts (tokens) to share a common set of standard. For example, to enable the token to define the total supply of tokens, “totalSupply” would be used, instead of “totalNumber” or “totalTokens”. Compliance to the standards avoids confusion and enables the token to interact with wallets, exchanges and different smart contracts without running into issues due to individual token differences.
The set of functions defined by the ERC-20 standard are:
totalSupply - get the total token supply balanceOf - get the account balance of account address transfer - send amount of tokens transferFrom - define where the tokens are transfering from approve - allow tokens to be withdrawn from sending address allowance - returns the remaining tokens of the address
A list of ERC-20 Token is available on Etherscan