Frustrating describes something that blocks you from doing what you want to do, leaving you feeling annoyed, stuck, or defeated. When you're trying to solve a math problem and keep getting the wrong answer, that's frustrating. When you're building something and a piece keeps falling off right when you almost have it done, that's frustrating too.

The feeling comes from the gap between what you're trying to accomplish and what's actually happening. A frustrating video game level is one where you can see what needs to be done but can't quite do it. A frustrating conversation happens when you know what you want to say but can't find the right words, or when someone keeps misunderstanding you.

What makes something frustrating, rather than just difficult, is that sense of being blocked. Difficult things challenge you but let you make progress. Frustrating things feel like hitting a wall over and over. A puzzle can be difficult without being frustrating if you're learning and advancing. But if you're missing one piece, or the instructions are unclear, or you keep making the same mistake without understanding why, that difficulty turns into frustration.

The related noun is frustration: that hot, uncomfortable feeling when things won't work the way you need them to.