Uninformed means you do not have enough knowledge or facts about something — so your opinion, guess, or decision is built on nothing solid. The important thing is that it is about missing information, not about being stupid. A very clever person can be completely uninformed about a subject they have never studied. We often attach it to the thing produced rather than the person: an uninformed opinion, an uninformed comment, an uninformed decision, an uninformed voter. When someone says 'that's an uninformed opinion', they are saying 'you are talking about something you haven't looked into' — it is a criticism, and often a sharp one, though it is dressed in calm words. It also appears in the phrase 'uninformed consent' (and its opposite, 'informed consent') in hospitals and research: agreeing to something without being told what it really involves. Compare it with 'ignorant', which in English can sound insulting about the whole person; 'uninformed' points only at the gap, and can even be used about yourself with no shame: 'I'm completely uninformed about football.'