Thank you all very much for answers. I think I understand now.

Another question about Ledger nano s is what is the mechanism of "attach to pin"?

I have tested with restoring a new HW wallet with my seed and successfully get back with the secret phrase attached to pin.

My question is if this can work on different HW wallets, will it also work on Electrum?

For example, if I import my private seed to Electrum, and then I should also input the secret phrase.

Does it work like BIP38?