The OUSD smart contract aggregates all users' stablecoin deposits into a single pool of investable assets. Funds are then allocated across one or more earning strategies at any given moment in time. The Vault favors high-yield strategies but also seeks to maintain diversification across multiple strategies. Diversification removes single points of failures and mitigates risks.
In contrast to Yearn Vaults, TokenSets, or Zapper opportunities, users do not select individual strategies. All deposited stablecoins and consequently all OUSD tokens are fungible.