Miniscule amounts of Bitcoin in a wallet — with a value that would be outweighed by the cost of a transaction fee.
This cumbersome collection of particles with little or no value may seem a perfectly innocent and acceptable by-product of digital currency, but it can be used in ways considered harmful to financial networks.
More often than not, the value of dust in a dust transaction will be significantly lower than the actual fee for moving the tiny particles. In many cases, this is the reason why these fractions end up gathering across wallets and rarely see the light of day.
Occasionally, a significant number of separate dust transactions will be maliciously used in what is known as a dusting attack — a deliberate act of transferring almost unnoticeable amounts of cryptocurrency to random wallets in order to then track activity within the wallet and break down the anonymity of its owner.
However, dust transactions are not entirely used nefariously. There are some charitable organizations, such as Dust Aid, which allow users to sweep up pockets of dust from their wallets and donate them to good causes.