When you debrief someone, you interview the person about an experience, project, or mission they've completed. A soldier's commanding officer might debrief her after a particularly difficult battle.
Spies and military personnel might expect their superiors to debrief them after a mission — the process is called a debriefing, and it includes questions about the experience and instructions about which details must be kept classified. Educators and counselors sometimes also debrief people, particularly those who have experienced tragedy or trauma, and who can be helped by talking through their experiences. The word debrief emerged at the end of World War II, originally as a military term.