What is Bitcoin Dust?

When a bitcoin wallet contains certain amount of bitcoin that is lesser than the limit for a bitcoin transaction to propagate on the network, this is referred to as Bitcoin Dust. It's an amount of bitcoin lying in a wallet which is impossible to spend.

Bitcoin dust is relatively small that it cannot even cover up for the transactions fee required to send bitcoins on the network. Miners who validate transactions won't confirm bitcoin dust if it's being sent on the bitcoin blockchain because it can't also cover up for their miner's fee.