The word “folly” occurs 23 times in Proverbs and only 16 times in the rest of the Bible. The dictionary defines folly as “a lack of good sense, understanding, or foresight; an act of foolishness; or a costly undertaking having an absurd or ruinous outcome.” I think that is exactly what Solomon had in mind as he advised against folly.
Over half of Proverbs’ verses that include “folly,” also pair it with the word “fool.” That gives the perspective that folly is foolishness.
Interestingly, in one instance, Solomon personifies “folly” as a woman who is loud, undisciplined, and without knowledge. That is a most effective metaphor, explaining why folly is to be avoided.
Of course, there are the simple who may desire a woman like Folly, but that just wouldn’t be prudent — and Solomon repeated cautions against liaisons of that nature.