A stablecoin is a cryptocurrency designed to hold a stable value, usually pegged 1:1 to the US dollar. How that peg is maintained varies significantly by design, and the differences matter for how much risk a holder is actually taking on.
Fiat-collateralized stablecoins
The most widely used stablecoins are backed by reserves of cash and short-term government debt held by a central issuer, who mints and redeems tokens 1:1 against those reserves. The main risk here is counterparty and custodial: holders are trusting the issuer's reserves and audits.
Crypto-collateralized stablecoins
These are backed by other cryptocurrencies locked in smart contracts, typically over-collateralized to absorb price volatility in the collateral itself. They remove the need to trust a single custodian, but they inherit the volatility and liquidation risk of the underlying collateral.
Algorithmic stablecoins
These attempt to hold a peg through incentive mechanisms and token supply adjustments rather than hard collateral. This category has produced some of the most significant failures in crypto history when confidence in the mechanism broke down, which is why regulators now scrutinize these designs most closely.