What does ERC-20 mean?
ERC-20 refers to the standard created for tokens which are launched on the Ethereum network, which guarantees that they will remain secure and behave in a predictable manner.
The ERC-20 standard has allowed for the easy transfer of compatible tokens. One heavily utilized use case for this is in the transfer of Ether in the ICO process.
Another benefit of this type of standardization is that exchanges and wallets only need a single contract address in order to manage any of the tokens which are ERC-20 compatible.