After entering a Passphrase the next screen before confirming shows the beginning of the passphrase and a Fingerprint, the later being derived from the former. What exactly is this fingerprint? Is it comprable to the 2 security words which show up after entering the first 4 characters of the PIN when opening Prime? Do I securely save it like other seeds or passwords? What do I do with it, if anything?
When you apply a passphrase it creates a completely separate wallet, and the fingerprint is a short ID for that specific wallet. The same passphrase always gives the same fingerprint; change one character and it’s totally different.
Its job is to confirm you typed the passphrase correctly. There’s no such thing as a “wrong” passphrase, any entry is valid and just opens a different wallet, so a typo won’t error, it’ll quietly take you to a different empty one. If the fingerprint matches what you saw last time, you know you’re in the right wallet.
It’s a similar idea to the two security words, but a different job: the security words confirm the device hasn’t been tampered with, while the fingerprint confirms your passphrase and which wallet you’re in.
You don’t need to save it like a seed. It’s not secret (it’s derived from public info, so it can’t be used to access funds) and it isn’t needed for recovery, your seed plus passphrase rebuilds everything. Most people just note it or remember it as a quick “right passphrase, right wallet” check.