IIRC it's called a passphrase. It's a backup of your wallet that is encrypted. It means you can not use that to import your address in another wallet. If you want the accessible backup, export your privatekey and save it in a document or print a scannable version of it so you can import it in any allet which supports address importing.
No it isn't. It's a seed. You can use it in any other wallet that works similarly and the same addresses and coins will be in there. It's all you need to backup or move your coins wherever you want if it's BIP 39 or 44 like Trezor and a few others.
Thanks for clarifying that. I may have been talking about the privatekey you can get on the PDF file, that one is the one that is encrypted with a passphrase right? Passphrase is the letters?
Yes, that was long time ago, before mycelium switched to being a HD wallet.
There you would get an encrypted backup and plus a password consisting of some letters.
Now mycelium is BIP32, BIP39 and BIP44 compliant, and you can totally import your mycelium backup word list on a trezor and vice versa, for example.