An advantage of terrain occurs when military personnel gain an advantage over an enemy by using or simply in spite of, the terrain around them. The term does not exclusively apply to battles and can be used more generally regarding entire campaigns or theaters of war.
Mountains, for example, can block off certain areas and make it unnecessary to station troops within the inaccessible area. That deployment strategy can be applied with other formidable environmental features as well, such as forests and mountains. In the former instance, dense vegetation can provide concealment for tactical movements such as setting up an ambush. In the latter, the elevation can provide an advantage to soldiers using projectile weapons, such as arrows or artillery pieces. Elevation itself is perhaps the most well-known example of terrain advantage, with gravity working to the advantage of the more elevated party.
Securing a terrain advantage is an important consideration for modern commanders, particularly those engaged in unconventional tactics such as guerrilla warfare, but it was likely of even greater concern for pre-industrial forces since the lack of mobility during first-generation warfare left soldiers very vulnerable to its effects. The ancient military strategist Sun-Tzu, for example, dedicated an entire chapter in his treatise The Art of War to terrain and situational positioning.