NIP is just Nostr Improvement Possibility. The building blocks of how Nostr works are all NIPs of various numbers. Users don't need to know what a NIP is or what any specific NIP is for.

You used a kind 1 note defined in NIP-01 to respond to me, and you had no idea of either. Your client didn't ask you if you wanted to create a kind 1 note. It just presented you with a reply button.

Good design will obfuscate these technical terms away in your client.