The term 'PART OF A MILITARY FORMATION' can be summarized as the word 'FLANK', which is a five-letter word. Flanking is a military tactic used to protect the sides of a formation from attack. It involves positioning troops on either side of the main body of troops in order to provide additional protection and to prevent an enemy from outflanking the main force. Flanking is often used in combination with other tactics such as frontal assaults, ambushes, and encirclements.