The Ethereum network has several different token options, each with their own set of rules and functions. The most common, after ETH itself, is the ERC-20 token. This particular token can be sent and received, as well as hold value (similar to BTC, ETH, LTC, etc).
How it differs from these other cryptocurrencies is that it operates off of the Ethereum network, while BTC is hosted by the Bitcoin blockchain. This means that the token, no matter what its name might be, is sent and stored using Ethereum addresses, transactions, and wallets. They also require gas in order to be sent and received.
ERC-20 stands for Ethereum Request for Comment, and 20 is the proposal identifier.
Many cryptocurrencies or stablecoins that you might know of are actually ERC-20 tokens. Most notably is Tether (USDT), the stablecoin pegged to the US dollar and in the top 5 biggest cryptocurrencies based on market cap. Others include Binance Coin (BNB), Maker (MKR), Basic Attention Token (BAT), USD Coin (USDC).