vanguard: Meaning and Definition of

van•guard

1. the foremost division or the front part of an army; advance guard; van.
2. the forefront in any movement, field, activity, or the like.
3. the leaders of any intellectual or political movement.
4. (cap.)a U.S. three-stage, satellite-launching rocket, the first two stages powered by liquid-propellant engines and the third by a solid-propellant engine.