A conjunction indicating that something happens contrary to what was stated or expected — used to express 'and yet', 'despite that', or 'however'.
雨が降っているのに、彼は傘を持ってこなかった。
Even though it's raining, he didn't bring an umbrella.
試験勉強をたくさんしたのに、点数が伸びなかった。
I studied a lot for the exam, yet my score didn't improve.
約束したのに来なかったから、少し怒っている。
He promised to come but didn't, so I'm a bit angry.