To rehash something means to present the same ideas, arguments, or material again without adding anything new or meaningful. When a teacher asks students to discuss a book and they just rehash what was said in yesterday's class, they're repeating the same points instead of developing fresh insights. When a movie sequel feels like a rehash of the original, it copies the same plot and jokes rather than offering a new story.

The word suggests a kind of lazy repetition. Imagine reheating yesterday's dinner instead of cooking something new: that's the feeling of rehash. If two friends keep rehashing an old argument, they're going over the same complaints without making progress toward understanding each other.

Rehash can be used as a noun too. You might say “The presentation was just a rehash of last week's material” or “I don't want to sit through another rehash of that debate.” The word often carries a hint of disappointment or criticism, suggesting that people expected something original but got the same tired repetition instead.