If someone is clueless, they do not understand what is going on — and the speaker is not being kind about it. It is stronger than a plain “I don’t know.” It often means “you have not even started to see the point,” or “you are living in another world.” Parents say it about teenagers; workers say it about a boss who never asks; friends say it with a laugh, but it can still sting. You can be clueless about one thing (“clueless about money”) or clueless in a wider way. Informal. The softer version is “doesn’t have a clue.” Calling a person clueless usually shows you are tired of their not knowing, or you think they should know.