Can anyone explain me what is a metasyntactic variables?

Answer 1

Searching is a good way to get knowledge. Please seach "metasynatactic" via google, or in wiki, you will get the answer you required. As my opinion, these words are usually used in examples in particular computer language. That means you can use any other proper words to replace them. But the teacher/book-author would like to use them in teaching or examples.

Answer 2

They are variables used as placeholder names in examples code to demonstrate something.