it is not that; it does not necessarily mean thatUsually appears as わけではない after a clause. It partially negates or corrects an assumption, meaning that something is not necessarily the case. The kanji 訳 is less common than the hiragana わけ in this expression.
JA: すべての人がその本が好きだという訳ではない。
EN: It is not the case that everyone likes that book.