Dust refers to a bitcoin wallet that contains such a small amount of satoshis that if it were to be sent to another wallet, it would cost more in transaction fees than actually sending it.
As a general rule, it’s a good idea to make sure you have a decent amount of sats in your wallet before you send so you can cover the costs. Some wallets allow you to set custom fees which can make things more affordable if you are using the main chain.
However, if you are not sending more than 0.01 BTC at a time, using the Lightning Network will facilitate small transactions with very low fees so you don’t have to worry about dust-amounts.