Stablecoins are a type of altcoin designed to have a stable value, typically pegged to a traditional currency like the US dollar or a commodity like gold. Examples include Tether (USDT) and USD Coin (USDC). Stablecoins aim to combine the benefits of cryptocurrencies, such as fast transactions and decentralization, with the stability of traditional currencies. They can act as a hedge against the volatility of other cryptocurrencies and play a crucial role in facilitating transactions within the crypto ecosystem.