The ERC-20 address is the Ethereum token standard used for Ethereum smart contracts. It stands for Ethereum Request for Comments. Developed in 2015, ERC-20 defines a common list of rules that an Ethereum token has to implement. This gives developers the ability to program how new tokens will function within the Ethereum ecosystem. This token protocol is the same on all ERC-20 tokens. One of the most revolutionary applications has been the tokenization of fundraising. For example, read about the identity management system CIVIC and how they incorporated tokens to grow their platform.
Some examples of ERC-20 tokens are:
MyEtherWallet is a great resource for ETH and token-related questions, as well as a place to store all your ERC-20 tokens. They offer a wide array of information that you can access here.