Resale royalty is a percentage that you will receive if your NFT sells on a secondary market. It is part of the smart contract and most NFT marketplaces respect it.
For example, you listed your NFT for 0.1 ETH and it sold. A collector then sells it for 2 ETH, if your resale royalty is 10%, you will automatically receive 0.2 ETH.
On Sloika you can choose your own resale royalty.
It is on-chain and a part of your own smart contract, and it is respected by a broad range of marketplaces, such as Opensea, Coinbase NFT, Rarible, LooksRare, Zora, and others.