Where is BTC server?

Excuse me, I'm a bit confused about something. Could you please clarify for me? When people talk about Bitcoin, they often mention a "BTC server." But as I understand, Bitcoin is a decentralized cryptocurrency, which means there's no central server or authority controlling it. So, where exactly is this "BTC server" that people keep mentioning? Is it just a misunderstanding, or is there some specific service or infrastructure that people are referring to? Thank you for your help in clearing this up.