An after-action review is like when you finish playing a game or activity and then you talk with your friends or parents about how it went. It's a way to see what went well and what didn't go so well.
Imagine you and your friends played a game of soccer in the park. After the game is over, you might all sit down together and talk about what you thought about the game. You might say something like "I liked how we worked together as a team," or "I think we could have passed the ball more instead of trying to score all by ourselves."
An after-action review is when a group of people, like a team or a group working on a project, take time to talk together about what happened during the activity they just finished. They might talk about what worked well and what they could improve for next time.
This can be really helpful because it helps everyone get better at the activity, whether it's playing a game, doing a project, or even something like cooking a meal. It's like taking notes on what went well and what didn't go so well, so you can be better prepared for next time.