Swap like swapping of blockchain e.g from ETH to EOS or to mainnet, it simply means the cryptocurrency is migrating from one blockchain to another (most times from a third party blockchain to their very own blockchain).
I just want to add, it can also be swapping within the same blockchain but different contract address.
Why they (the project/dev?) need to swap the token?
In addition to what Brainboss already said, some devs do this to fix an existing issue with their smart contract.