Omniscient means knowing everything. Someone who is omniscient has complete knowledge of all facts, events, and truths, with no gaps or mysteries.

In stories, an omniscient narrator knows everything about every character: their thoughts, feelings, past actions, and future plans. This narrator can tell you what the hero is thinking in one chapter and what the villain is plotting in the next, even though the characters themselves don't know about each other. Many classic novels use omniscient narration, giving readers a god's-eye view of the entire story.

In religious discussions, people often describe God as omniscient, meaning God knows all things past, present, and future. This differs from human knowledge, which is always partial and limited. You might know a lot about dinosaurs or chess, but you're not omniscient about them: there are still things to learn, details you've forgotten, or questions you can't answer.

The word is sometimes used playfully when someone acts like they know everything. If your friend claims to know exactly what will happen in tomorrow's soccer game, you might joke, “What are you, omniscient?” You're pointing out that nobody can actually know the future with perfect certainty.