The term "frontier" refers to a boundary or edge that separates different areas, often associated with unexplored or undeveloped regions. Historically, it has been used to describe the advancing edges of civilization, such as the western frontier in the United States during the 19th century, where settlers moved into new territories. In a broader sense, "frontier" can also refer to the limits of knowledge or exploration in various fields, such as science and technology. For example, the frontier of space exploration involves the ongoing efforts to discover and understand the universe beyond Earth.