Deletion means removing something completely, taking it out so that it no longer exists in that place. When you delete a sentence from your essay, you erase it entirely rather than just crossing it out or moving it somewhere else. When you delete a photo from your phone, it disappears from your photo library.

The word is often used in computers and writing to mean permanent removal. If you accidentally delete your homework file without saving a copy, it might be gone. This makes deletion different from hiding something or putting it away: deleted things don't exist anymore in that location.

In science, a deletion can mean a missing piece of something that should be there. Geneticists study deletions in DNA, where a section of genetic code is missing. In linguistics, deletion happens when sounds or words get dropped from speech, like how “going to” becomes “gonna” in casual conversation.

The opposite of deletion is insertion or addition. Most computer programs have an “undo” feature that can reverse a deletion if you catch it quickly, but once something is truly deleted and removed from storage, it can be impossible to get back.