Someone who is ill-informed does not know enough about a particular subject — not because they are foolish, but because they have not got the facts, or they have got the wrong ones. You can be a good student and still be ill-informed about how a medicine works, or about another country’s history. People use it in news, meetings, and arguments more than in kitchen talk. Calling a comment ill-informed is a polite but sharp way of saying “you are speaking without knowing.” Though actually, it usually points at one topic, not at a person as a whole: you are ill-informed about X. It is not a word for “always ignorant.”