𝗣𝗦𝗔:

"Bitcoin" is the overall network.

"bitcoin" is the currency.

Example:

"I used nostr:npub1tayp5jjjfqx4ufukxqamsl28wd5pggvteqe6u9n3svjn62lfr0hsp89l42 to study 𝗕𝗶𝘁𝗰𝗼𝗶𝗻, and then I bought 1 whole 𝗯𝗶𝘁𝗰𝗼𝗶𝗻!"