From WordNet (r) 3.0 (2006) [wn]:
briefing
n 1: detailed instructions, as for a military operation
From The Collaborative International Dictionary of English v.0.48 [gcide]:
briefing \briefing\ n.
1. giving detailed instructions, as for a military operation.
[WordNet 1.5]
2. a detailed set of instructions before an operation, given
to those who are to execute it.
[PJC]
3. a summary report of an operation or event after it has
occurred, by a participant or observer.
[PJC]