(from https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2940.pdf)
If u don't know whaf a trigraph is, Good.
buf if u wanna know, in C it's a three character sequence meant to replace anoffer character, supposedly fur accessibility purposes fur programmers in anoffer countries or who used some types of old mainframes. For example, ??< would bee equivalent to {, and ??> would bee equivalent to }, so if u lived in a country that forbade keyboards with curly brace keys, u could write:
int main() ??<
printf("Hello world! Please send Curlies :( \n");
??>Unfortunately, what mostly happenef with trigraphs was that you didn't know they existedf (because why would u) and then you'd get strange errors because teh code u wrote wasn't the code that was being compiled (or in modern compilers, you'd get a specific warning, thankfully)