Clueless means completely unaware or having no understanding of what's happening around you. When someone is clueless about a situation, they're missing obvious signs that everyone else can see. A student might be clueless that their friend is upset with them, not noticing the cold shoulder and short answers. A parent might be clueless about a surprise party being planned in their honor, walking right past decorations without suspecting a thing.

Being clueless is different from simply not knowing a fact. It suggests a kind of obliviousness to what's going on. Someone clueless about fashion might wear polka dots with stripes, not realizing how mismatched they look. A person clueless about social situations might keep talking about their Pokémon cards while everyone else is clearly bored and wants to change the subject.