Comment by int_19h

Well, "A4" doesn't imply anything about the intended use. The format of the name also implies that there is A3, A5 etc, both of which aren't all that uncommon either.

But, yes, for most people it doesn't really matter - you go to the store, you buy paper, you shove it into your printer, and it mostly just works. However, it's also not all that hard to run into situations where things break. E.g. most PDFs originating from US are rendered for Letter size paper, which means that printing them outside of US generally requires setting "fit size" rather than "original" to ensure that nothing gets clipped. Vice versa also happens, but because US is so culturally dominant, Americans rarely run into that particular issue.