The phrase “beyond the pale” dates back to the 14th century, when the part of Ireland that was under English rule was delineated by a boundary made of such stakes or fences, and known as the English Pale.
To travel outside of that boundary, beyond the pale, was to leave behind all the rules and institutions of English society, which the English modestly considered synonymous with civilization itself.
Today this phrase is an idiomatic expression referring to something outside the bounds of acceptable behavior.
1 Describing behaviour that is considered to be outside the bounds of morality, good behaviour or judgement in civilised company.
2 Fig. unacceptable; outlawed.