The term 'frontier' is used to describe a region at the EDGE of a settled area, often referring to the outermost limits of exploration and settlement. The crossword solutions for this term include 'OUTSKIRTS' (9 letters), 'PERIMETER' (9 letters), 'BACKWOODS' (9 letters), 'EXTREMITY' (9 letters), 'HINTERLAND' (10 letters), 'BACKCOUNTRY' (11 letters), 'BRINK' (5 letters), 'LIMIT' (5 letters), 'BUSH' (4 letters), 'MARCH' (5 letters), 'BOUNDARY' (8 letters), 'BORDERLAND' (10 letters), 'BORDER' (6 letters), and 'EDGE' (4 letters). All of these words refer to the outermost limits of a region, and can be used to describe the concept of a frontier.