I would not call it a token. Cashu is the protocol.

So cashu is chaumian ecash protocol on bitcoin. 

It works like having receipt of bitcoins that you store at a custodian. You can either put in more bitcoin and mint more ecash, or melt your ecash and get back your bitcoin. But this is done in a private way. 

 Cool, thanks 👍 

 This npub.cash thing is cashu protocol?