Oblivion is the state of being completely forgotten or unknown. When something fades into oblivion, it disappears so thoroughly from memory that it's as if it never existed. Ancient civilizations that left no written records or monuments vanished into oblivion. Inventions that nobody found useful, books that nobody read, and ideas that nobody shared can all sink into oblivion over time.

The word also means the state of being unaware or unconscious. A soldier knocked unconscious in battle might be described as in a state of oblivion, completely unaware of what's happening around him. Someone sleeping so deeply they don't hear their alarm clock is in oblivion.

Oblivion suggests something more complete than simply forgetting where you left your backpack. It's total erasure, like a sandcastle that waves wash away until no trace remains. When historians discover a lost city or archaeologists unearth forgotten artifacts, they're rescuing things from oblivion. The opposite of oblivion is remembrance: keeping something alive in memory. That's why people build monuments, write histories, and tell stories to prevent important people, events, and ideas from slipping into oblivion.