Military term for a unit sent ahead of the main force to scout, secure positions, or prepare the way. Also used figuratively for any group that goes ahead to pave the way.
The advance troops scouted the enemy's position.
They were sent as a vanguard to develop new markets.
Compound of 先遣 (せんけん, 'sending ahead') and 部隊 (ぶたい, 'unit, corps'). The term is a straightforward Sino-Japanese military coinage.