“Taint/ Tainted” is a term used to refer to digital assets that have never been cleaned/mixed/ tumbled.
Tainted assets have long history trails that are easy to follow.
example:
Wallet 123a sent Wallet 999a 0.5 Bitcoin. When looking at the transaction on the block explorer, those 0.5 Bitcoin point to Wallet123a that points to Wallet321a that points to Wallet456a. Turns out that Wallet456a is a blacklisted because they have been found to be scamming people. Those 0.5 Bitcoins are in theory sieazble by local governments.