What is foo?

Question

I am seeing Foo for a while now; what exactly Foo is?

Answer 1

It's a 'metasyntactic variable'.

When you want to quickly explain a few lines of code, usually you need variables, too.

How to name them? x? y? some_list? var?

All possible, but at the same time there's the 'custom' to use a set of always the same funny names.

For example in Python you see 'spam' and 'eggs' used everywhere - a Monty Python reference.