A vault is a contract each user generates for their wallet address, which they are the owner of. This contract can hold NFTs and fNFTs in a custodial state for both sales and auctions. An individual's vault its owner to sell their NFTs from the vault if they wish as well as withdraw any NFTs/tokens received from airdrops at any time as well as making things simpler to grab information like the number of unique holders & true owners of NFTs.
NFT Vaults on PaintSwap allow the platform to have the best of both worlds of custodial and non-custodial listings. For NFTs with changing values and underlying assets the NFT vault allows a safe and secure way for buyers to know the NFT hasn't been changed or had value removed in between its listing and the sale.
Vault usage is optional, except for auctions, but is recommended for fNFTs like Solidly veNFTs, Revest Finance & Liquid Driver NFTs. They can also be used for peace of mind knowing that you will not be susceptible to a bad sale when transferring a listed NFT without cancelling the listing, and then receiving it again later down the road where it could be snapped up if the old listing has not expired.
Each user will generate their own vault contract the first time they interact with the PaintSwap marketplace. This gives the user access to their vault and any items in them be it NFTs or tokens that have been airdropped to holders.