Ecash is money as a piece of text that you can just copy and paste or transmit with a QR-code or with a private message or however you want. It's a bearer asset: you have the piece of text = you have money. Usually ecash is an IOU but European Union plans to issue euros as ecash as well.

Mint is anything that issues ecash. It's the job of the mint to prevent double spending. When you receive ecash, you need to contact the mint to make sure it wasn't already spent. If it wasn't, you get fresh ecash of the same value. If you want, the old coin is melt and a new coin is minted, hence the name.

Fedimint is the software for running a mint as a group. A group mint running fedimint is also called fedimint because "fedimint-running mint" sounds stupid. Cashu is the software for running a solo mint. Fedi is the app to use fedimints.

Can't agree here. Fedi is very user-friendly. In comparison, XMR mobile wallets need you to sync the chain all the time. With ecash you can push money: "here, scan this, here's 1k sats for you" but with XMR you can only pull ("give me your address so I can send you some piconeros"). Mint transactions are final in seconds, there's no waiting for the next blocks to confirm.