A frontier is the edge of settled or explored territory, where civilization meets wilderness. When American pioneers pushed westward in the 1800s, they called the unsettled lands ahead of them the frontier. Beyond the frontier lay vast stretches of land that hadn't yet been mapped, farmed, or built upon by the arriving settlers.

The word captures that feeling of standing at a boundary, looking toward something unknown and full of possibility. Frontiers exist in more than just geography. Scientists talk about pushing the frontiers of knowledge when they explore questions no one has answered before. When engineers develop new technology, they're working at the frontier of what's possible. Space has been called “the final frontier” because it represents the ultimate unexplored territory.

A frontiersman or frontierswoman is someone who lives and works at the edge of settled territory, skilled at surviving in challenging conditions. The frontier spirit refers to qualities like courage, self-reliance, and willingness to venture into the unknown. Something cutting-edge or pioneering can be described as at the frontier of its field.