In English there is a saying of foo & bar, which means anything goes, just occupy a position first, and you can replace it with something else later. Especially in programming languages, you need to occupy a position first, but you cannot replace it with a space, because later when you want to add a more meaningful word or variable, it is easy to find and replace it. What is used at this time is Placeholder. There is a similar saying in Japanese, which is HogeHoge, ほげほげ.