Dust

Dust is a bitcoin amount so small that spending it would cost more in transaction fees than the amount is worth. Bitcoin Core's default relay policy treats outputs below 546 satoshis as dust for standard address types and refuses to relay transactions that create them, a threshold that shifts with the fee environment and script type.

Why it matters

Dust is a byproduct of Bitcoin's accounting model. Balances live as discrete unspent transaction outputs, or UTXOs, and spending each one carries a size cost in the transaction. An output worth less than its own spending cost is economically stranded, cluttering wallets and swelling the UTXO set every node must store. Wallets manage this through coin selection and by consolidating small outputs when fees are low.

Dust also has a security dimension: attackers deposit tiny traceable amounts in many wallets, hoping owners will unknowingly combine them with other coins and expose their address clusters, a privacy risk known as a dust attack.

In the gold vs bitcoin debate

Gold has its own dust, literally. Flakes and fractional grams below dealer minimums carry premiums and assay costs that make them uneconomical to trade, just as sub-546 satoshi outputs are uneconomical to spend. Both cases show the same principle, that transaction costs put a floor under any money's practical divisibility. Bitcoin's second layers, such as Lightning, push that floor far lower than physical metal can go.