If you are unimpressed by something, you looked at it, you understood it, and it did not move you. You are not angry and you are not confused — you just do not think it is good, or clever, or exciting. The word almost always describes a person's reaction: 'She was unimpressed by his new car.' We usually build it with 'by' or 'with' after it. It is a very English kind of politeness: instead of saying 'that was bad', we say we were unimpressed, and everyone understands that this is the softer, cooler way to say the same thing. Because of that, it often sounds stronger than it looks — a boss who says 'I was unimpressed with your report' is not being gentle. There is also a slightly different everyday use, common when people talk about children, parents, or officials: 'My mother was distinctly unimpressed' can mean she was not pleased, close to annoyed, not merely neutral. Notice too that being unimpressed needs something to react to. You cannot be unimpressed by a thing you never saw. That is what separates it from simply not caring.