Pioneer originally referred to a person who is among the first to explore or settle a new country or area.
In modern usage, pioneer can mean:
1. A person who is among the first to research and develop a new area of knowledge or activity
2. A soldier or other person who prepares the way for others, especially by going ahead to repair roads, clear obstacles, etc.
3. In ecology, the first species to colonize a previously disrupted or damaged ecosystem
4. A brand of audio equipment (Pioneer Corporation)