A name for a kind of position in a battle between two (or more?) armies where one side gets pressed from two sides which are at an angle (close to 90 degrees) to each other. In other words, the pressed side\army is what one might call cornered by the other sides forces. Let me try to examplify this:
Both these illustrations illustrate a dogleg front. If A represents one side (the attacker) and D the other (Defender), one can see that A has successfully forced D back on one side, forcing them to make a dogleg font.
This could happen (for example) if one army has an advantage on one flank of the battlefield and is able to press it's enemy there, or if one of two equally strong armies should recieve help from allies attacking the enemy from one side, as happened in The Battle Of Waterloo, where Napoleon suffered his final defeat.