noun which may take the genitive case particle 'no', na-adjective, noun
ignorant of the ways of the world; naive; unworldly
Describes a person who lacks practical knowledge of society, often implying innocence or inexperience rather than stupidity. Can be used as a noun or adjectivally with な or の.
彼は世間知らずで、すぐに人を信用してしまう。
He is naive about the world and trusts people too easily.
That way of thinking is the height of naivety.