What is a CTC number?

Excuse me, I'm quite intrigued by the mention of a CTC number. Could you please elaborate on what exactly a CTC number is? I'm wondering if it's some kind of special identifier or code that's unique to the cryptocurrency or finance industry. Is it used for regulatory purposes, or does it serve a different function? Any insight you could provide would be greatly appreciated as I'm trying to expand my knowledge in this area. Thank you for your time and assistance.