Why are many examples of variables or files named after bar or foo?

the problem is that when I went to ES6, I saw let bar;let foo. , and then I named it with bar.html,foo when I first went to MDN to read the homologous policy. Do these two English have special meaning?
as shown in the picture.
clipboard.png
though bored, is pure curiosity . :)

Mar.29,2021

these two words are equivalent to our "Zhang San" and "Li Si". You can refer to this: https://blog.csdn.net/deargua.

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