Monero is the leading cryptocurrency focused on private and censorship-resistant transactions. The majority of existing cryptocurrencies, including Bitcoin and Ethereum, have transparent blockchains. Transactions can be verified and/or traced by anyone in the world. This means that the sending and receiving addresses of these transactions could potentially be linked to real-world identities.
Monero, on the other hand, uses various privacy-enhancing technologies to ensure the anonymity of its users. Unlike selectively transparent alternatives (e.g. Zcash), Monero is the only cryptocurrency where every user is anonymous by default. The sender, receiver, and amount of every single transaction are hidden.