What is hash key on Iphone?

Could you please explain to me what exactly is a hash key on an iPhone? I've heard it mentioned in the context of security and encryption, but I'm not entirely clear on its specific purpose or function. How does it help to protect the device and its data? Is it something that can be easily accessed or changed by the user, or is it more of a secure, hidden feature? And finally, how does it differ from other security measures like passwords or Touch ID? I'd really appreciate a clear and concise explanation of this term and its role in iPhone security.