Oblivious means completely unaware of something, even when it's obvious to everyone else. You're not paying attention or simply don't notice what's happening around you.

Picture a student walking down the hallway, headphones on, humming along to music, completely oblivious to friends calling their name and waving. Or imagine someone so focused on reading a book that they remain oblivious to the fact that everyone else has left the room. Being oblivious means missing something that's right there in front of you.

Sometimes people are oblivious to things that don't matter much: you might be oblivious to a small stain on your shirt. But being oblivious can also mean missing important signals. A teammate might be oblivious to hints that others are frustrated with their behavior. A friend might seem oblivious to how their jokes affect someone's feelings.

The word often implies that you should have noticed what you missed. If your teacher hasn't told you about tomorrow's field trip, you're not oblivious to it. You're just uninformed. But if she's announced it three times while you daydreamed, then you're oblivious. You can be oblivious to something (the noise outside) or oblivious of something (the passing of time).