若非 (correct pronunciation: ruò fēi, though this row's pinyin field says rě) is a formal conjunction meaning 'if not' or 'unless'. It typically appears in written or formal spoken Chinese to introduce a hypothetical condition that is contrary to fact, followed by the result or consequence. You will often see it in structures like 若非…，就… ('if not for X, then Y'). Because it is a function word, its bare gloss gives little guidance on usage — remember it always opens the condition clause and sets up a contrastive outcome.