What does abc mean?

If you mean ABC, which is often mentioned in variety shows in Taiwan Province Province.

So it refers to "returnees"

Returnees here refer to people who grew up in English-speaking countries and returned to Taiwan Province Province. It's called ABC. Because they say ABC has grown up. Sometimes it is also called ABC to return from studying abroad;

If it is a general synonym, it can be understood as the meaning of simple foundation. Because ABC is the first three letters of English, it can represent the beginning!