Because of Electrum and some other wallet that support custom seeds, I'll just simply put it as 12 words upwards ( although the 12, 15, 18, 21 or 24 words are the normal default ones)
Electrum does not support custom word unless it is BIP39.
BIP39
proposal is what I am referring to. They are 12, 15,
18, 21 and 24 words long. Not
lesslesser not longer. Shorter is not secure while longer is not proposed. Nothing in-between but 12, 15,
18, 21 and 24 and that is what you will on BIP39 wallets. 12 words is
comingcommon, then followed by 24 words
, but some wallets like Sparrow support can generate all.
Seed phrase is important because it can generates the private key which can be used to recover your coins or to spend the coins.
Aside frome this people prefer to work with seed phrases because they are easier to manage, store and work with. But private keys are very important when it comes to things like coin control.
I mean what that is most important is the private key, even seed phrase is important because of the private key that it can generate. That is the work of seed phrase. It is easy to backup
which is the reason it is proposed and named mnemonic.