What is the meaning of "Zongdi" in calligraphy? Is it a polite expression?

What is the meaning of "Zongdi" in calligraphy? Is it a polite expression? Friend: Hello! "Zongdi" is a polite term, not a polite one. Why do you say that? There are two reasons: 1. Same disciple. That's rude, isn't it? 2. They are all readers, so the title looks very close and polite. What did you say?/Sorry?