The word all means every single one, with nothing left out. When you eat all your vegetables, you finish every last carrot and broccoli floret on your plate. When a teacher says “all students must turn in their homework,” she means every student in the class, without exception.

All appears everywhere in English, often in phrases that add emphasis or clarity. When something goes wrong, we might say “all is lost” to express that everything feels ruined (even if it's not quite that dramatic). When someone gives maximum effort, we say they gave it their all. If you're all in on a plan, you're completely committed to it, holding nothing back.

The word can also mean “completely” or “entirely,” as in “I'm all finished” or “She's all grown up now.” Sometimes it appears in phrases where it means “only” or “nothing more,” like when you say “That's all I wanted to say.”

All is one of those small, powerful words that shows up constantly in speech and writing. It's the difference between “some cookies are left” and “all the cookies are gone.” That complete sweep, that sense of totality with zero exceptions, is what makes all such a useful and important word.