What is a privacy coin? This term has been around since almost the beginning of crypto, and few are more contentious. In the early days it was something people avoided due to regulators, but now, due to the privacy pump, everyone wants to be one! But what concretely is the definition? Well first, the term is kind of meaningless! So many different features matter in crypto: usability, speed, scalability, security, programmability, etc. No one-trick pony will ever survive. Eventually (as in, in the next five years), every coin will need privacy features, so "privacy coin" will be meaningless. But it's a term, so we need a definition. This is the best I've got: Any cryptocurrency that has built-in, explicit privacy features that go beyond what Bitcoin has built-in. Clearly this includes Dash, Monero, and Zcash, the three classically known for this. But what about Decred, Litecoin, and Bitcoin Cash? Well, Decred has a CoinJoin similar to what you can do on Bitcoin, but it's actually built into the protocol, so I'd say it counts as a privacy coin. Litecoin has actually pretty good privacy with MWEB. The one snag is that it's soft-forked into the network, so it's only built in to the network that has upgraded (it's possible to run Litecoin nodes that don't support MWEB). But still, it's a protocol feature, so it counts. Probably Bitcoin Cash is where I'd draw the line: it has a CoinJoin similar to Decred, but it isn't part of the protocol itself, it's a separate service. In terms of privacy this doesn't really matter, but because it's not offered by the network itself, I'd say it would fall outside of the definition of a "privacy coin." But really, all that matters is privacy. You can use Bitcoin with a decent level of privacy with the right tools. Smart contracts on Ethereum and Solana can provide better privacy than protocol-integrated CoinJoin features, even though they couldn't be considered "privacy coins." So there you have it. I hope that clears some things up.