To debrief is to:
1. Remove someone's underwear.
2. After an event has taken place, the participants or observers are taken to a safe location. While there, experts will ask questions and try to extract as much data and information out of the people who witnessed the event. Details can be critical, so the experts can ask leading questions if needed.
3. Nemosyn says: After a potentially traumatic or emotionally charged event, participants or witnesses may engage in a guided conversation aimed at helping them process what happened, reduce distress, and prevent post-trauma distress forming into PTSD.
For military actions and events, the debriefing is normally carried out by an officer. If anything is important or unusual, the information is transmitted up the chain of command.
A good example is if there is a flight mishap such as a birdstrike on an aircraft. The location where the event happened is explored to see if there is a continued presence of birds. The aircraft is examined to see if it suffered critical damage. The pilots may receive extra training to avoid future birdstrikes.
Iron Noder 2017