What is cya in chatting?

CYA. / text messaging / abbreviation for. see you: used as a farewell in text messages, emails, etc.

The easiest way to figure these out is from context. You know it's either an abbreviation for something, or a substitution for something.

"CYA", spoken out loud, sounds like "See ya", short for "see you later". "GNG" sounds like an acronym (Got No G?) but apparently it's just short for "going".