In the context of cryptocurrency, “dust” refers to a very small amount of cryptocurrency that’s left over in a wallet or account. These amounts are usually so small that they don’t meet the minimum network fee required to transfer them.
In the Bitcoin blockchain, for example, if you have a small amount of Bitcoin left in your wallet that is less than the fee required to send a transaction, that small amount is considered “dust”.
This term also applies to other cryptocurrencies as well, not just Bitcoin.