Abatis
A type of man-made obstacle used in trenchworks or fortifications. It consists of either a line of sharpened stakes, or cut tree limbs with sharpened branches and foliage oriented towards the enemy.
Casualty
Any loss in manpower that negatively effects a unit's fighting strength. This includes any soldier killed, wounded, missing or captured.
Enfilading Fire
The act of firing across the longest axis of an enemy unit or formation, allowing for maximum target density and reducing the number of enemy able to directly respond. It can be either flanking fire or frontal fire, depending on the enemy formation and direction of movement.
Salient
A bulge in a defensive line. While they can provide useful observation posts or jumping-off points for attacks, salients are comparatively isolated positions and are vulnerable to enemy assault from three sides. Salients can vary in size drastically, but the same basic principles still apply.