Privacy coins are cryptocurrencies that intentionally make it difficult to track transactions.

https://coinmarketcap.com/alexandria/article/what-are-privacy-coins

Most cryptocurrencies use a public ledger; a central feature is the public record of the flow of value from one wallet to another. Growing Know Your Customer (KYC) and Anti-Money Laundering (AML) requirements are making it much easier for governments to track your transactions.

Privacy coins resist this, providing anonymity similar to cash transactions but without the need for physical exchange. This makes them very effective for protecting the privacy of law abiding citizens – but it also makes it harder to fight money laundering and terrorism funding.