You have one master key (extended key) and can produce a lot of derived keys from it. But each derived key can be master key as well, so there is extended form for it.
Hello konovalets, thank you for the reply. So, let me see if I understand correctly? I have been studying the BIP32 page
BIP Extended Key -> many different Derived Private Key
Derived Private Key + chain code = Extended key
So, which key do I use to import into Electrum or something?
So does generation go like
Private Key -> BIP Extended key -> Child Key ?