Ecash is a technique to create digital money invented in the 80s by David Chaum
It was the very first concept of cryptocurrency (25 years before Bitcoin)
It's a bearer assets with amazing privacy properties, and in my opinion, it's the thing that is closest to physical cash in the digital realm
Ecash is not stored in a database or a blockchain. The money is represented as digital data that you (the user) store in your wallet. It is not like Bitcoin, where you store keys to move assets on a blockchain.
Historically, it had nothing to do with Bitcoin until some projects like Cashu started building it on top of Bitcoin.
In its current form, it allows us to build custodial Bitcoin applications with very interesting properties: amazing privacy, censorship resistant, and programmable to name a few.
Cashu is a protocol that describes how to build these things. All Cashu apps are interoperable.
Ecash mints are centralized: they are service providers (that can be single server or a federation of a handful) – Ecash is not decentralized!
But: we are lowering the bar of running mints so that many of these can be deployed, either for the purpose of serving a community, or for a specific website, app, whatever you can think of.
IMPORTANT: If you get ecash from a mint in exchange for Bitcoin, the Bitcoin are not in your control anymore. That means the provider can rug you! Be 150% aware of this and only use it accordingly (very small amounts, for daily spending, etc).
Shoot if you have more questions and check out https://cashu.space if you want to learn more.
Happy to give you a rundown:
IMPORTANT: If you get ecash from a mint in exchange for Bitcoin, the Bitcoin are not in your control anymore. That means the provider can rug you! Be 150% aware of this and only use it accordingly (very small amounts, for daily spending, etc).
Shoot if you have more questions and check out https://cashu.space if you want to learn more.