1. To give essential information to someone: "The reporters were briefed about the President's plan to run for another term."
2. To give someone all of the necessary information about something in preparation for a discussion or decision that will come later: "The President has been briefed by his economic advisers."
3. When someone briefs a person, or a group of people, he or she is providing information or instructions that are necessary for the recipient or recipients: "The captain of the ship briefed the crew about the new safety procedures."