Hello there! Have you ever watched a movie or a TV show that's not made up of actors pretending to be someone else? Something that tells a story about real-life people, places or events? That's what a documentary is!
Now, imagine there's a group of people who love watching and judging documentaries. They are called the Academy of Motion Picture Arts and Sciences (imagine them like judges of a competition). Every year, they watch lots and lots of documentaries that were released in the past year from all over the world.
After they watch all these documentaries, they have to choose the best of the best. The one that they enjoyed the most or the one they think is the most important or best made out of all of them is chosen as the winner of the Academy Award for Best Documentary Feature. This award is like a sticker that's given to the movie/documentary that they think is the best.
It's like when your teacher gives you a prize for being the best in your class. The winner of the Academy Award for Best Documentary Feature gets a golden statue (a trophy) to put on their shelf, and the director, producers, and other crew members get to walk on stage and give a speech saying thank you or telling us why they made the documentary.
So, in short, the Academy Award for Best Documentary Feature is an award given to the best documentary film of that year, by a group of judges who love and understand these types of movies!