Duplicate means to make an exact copy of something. When you duplicate a document on a computer, you create a second file with identical content. When a teacher duplicates worksheets on a copy machine, she makes enough copies so everyone in class gets one.

Scientists might duplicate an experiment to verify their results. Artists can duplicate a drawing by tracing it carefully. Video game players might discover a glitch that lets them duplicate valuable items in their inventory.

Duplicate can also work as a noun meaning the copy itself. If you lose your house key, a locksmith can make a duplicate. Libraries often keep duplicate copies of popular books so more students can check them out at the same time.

Sometimes the word carries a slightly negative meaning, suggesting unnecessary repetition. If two students accidentally do duplicate work on a group project, they've wasted effort by doing the same thing twice. And when someone fills out forms, they might need to submit them in duplicate (two copies of everything) or even in triplicate (three copies).

The key idea: duplicating means making something identical, whether that's useful (duplicating your important files as a backup) or wasteful (duplicate efforts that could have been avoided with better planning).