When an exchange sets a minimum tradable quantity for a particular coin, any amount below that value is known as "dust." For instance, Binance requires a minimum tradable quantity of 100 for certain coins. The amount of dust varies depending on the coin and often arises when trading fees are paid in that specific coin. For example, if a trader buys 110 coins but pays fees in that coin, they may be left with 108.5 coins. If they sell 105 coins, the remaining 3.5 coins may be considered dust by the exchange.