battle line

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun military, army The notional line on either side of which opposing forces are arrayed, and at which they meet in battle; a fortified line, short of the line where battle is expected, and behind which forces are arrayed; a forward line of infantry or other force, prepared for battle.
• noun military, navy A line of battle.
• noun figuratively, usually plural Any of those parts of a contest which, as a result of strategic decisions on both sides, are most closely fought and will likely determine the contest's course and outcome.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the line along which warring troops meet