A transaction output that is smaller than a typical fee required to spend it. This is not a strict part of the protocol, as any amount more than zero is valid. A bitcoin can be divided into one-hundred million pieces, known as satoshis . Very small denominations of bitcoins are known as dust as they have no practical value. Some websites, such as faucets , may attempt to make many dust transactions, which clutter up the blockchain. Small transaction fees and limits on how many satoshis can be sent have been imposed to limit dust transactions. Refusal to mine or relay dust transactions has been imposed to avoid unnecessarily increasing the size of unspent transaction outputs (UXTO) index. See UXTO .
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc