UserOp Mempool

Separate mempool for ERC‑4337 user operations maintained by bundlers, with its own fee rules, reputation limits, and validation pipelines.

User Operation (ERC‑4337)

Transaction‑like object used in account abstraction, containing calls, signatures, and gas limits, bundled by a paymaster/aggregator into on‑chain execution.

Uniswap v4 Hooks

Extensibility points that let custom logic run on pool events like swaps or liquidity changes, enabling features such as dynamic fees or on‑chain TWAMMs.

Uniswap v3 Concentrated Liquidity

Liquidity providers choose price ranges for their deposits, creating higher capital efficiency but requiring active management and exposing to range risk.

Uniswap

Automated market maker protocol enabling token swaps via liquidity pools; introduced constant‑product AMMs and later concentrated liquidity designs.

Undercollateralized Loan

Lending where borrowers post less collateral than the loan value, relying on credit scoring, real‑world enforcement, or guarantees beyond on‑chain liquidation.

Upgrade Key (Admin Key)

Privileged key or role with power to change implementations or parameters; centralization risk mitigated with multisigs, timelocks, and on‑chain governance.

UUPS Proxy (ERC‑1822)

Universal Upgradeable Proxy Standard where the implementation contract includes the upgrade logic; reduces proxy surface area compared to admin‑proxy patterns.

Upgradable Proxy

Proxy contract that delegates calls to an implementation address which can be changed by an admin or governance, enabling upgrades without migrating storage.

Upgradeability (Smart Contracts)

Design patterns that allow changing contract logic after deployment while preserving state, typically via proxies; increases flexibility but adds trust assumptions.

Uncle Block (Ommer)

Ethereum term for a valid block not in the canonical chain due to a race; referenced by later blocks for partial rewards, now called “ommer”.

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