Unconfirmed Transaction

Transaction that is broadcast and sitting in the mempool but not yet included in a block; may be replaced or dropped under congestion or policy rules.

Unstaking

Process of withdrawing staked tokens from a validator or pool; may trigger an unbonding period and forfeit rewards during that time.

Unbonding Period

Time delay between initiating unstake and when tokens become transferable, used to protect PoS networks from instant exit attacks or slashing evasion.

UTXO Dust

Very small outputs whose value is close to or below the cost to spend them; can bloat wallets and reveal addresses when later consolidated.

UTXO Consolidation

Combining many small UTXOs into fewer larger ones during low‑fee periods to reduce future transaction size, cost, and privacy leakage from change outputs.

UTXO Set

The current collection of all unspent outputs tracked by a full node; its size affects memory usage and initial sync time.

UTXO Model

Accounting approach where balances are represented by sets of spendable outputs rather than account states; enables parallel validation and simple verification.

Universal Approximation Theorem

Result showing that sufficiently large neural networks with non‑linear activations can approximate any continuous function on compact domains to arbitrary accuracy.

Unimodal Model

Model trained on a single modality such as text or images, as opposed to multimodal systems that process multiple input types together.

User‑in‑the‑Loop (UIL)

Interactive AI pattern where human input guides or corrects the model during or after inference, improving quality and accountability.

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