What does "reconnaissance" mean?

Reconnaissance: The act of reconnoitering; preliminary examination or survey. Specifically: (a) (Geol.) An examination or survey of a region in reference to its general geological character. (b) (Engin.) An examination of a region as to its general natural features, preparatory to a more particular survey for the purposes of triangulation, or of determining the location of a public work. (c) (Mil.) An examination of a territory, or of an enemy's position, for the purpose of obtaining information necessary for directing military operations; a preparatory expedition. Reconnoissance in force (Mil.), a demonstration or attack by a large force of troops for the purpose of discovering the position and strength of an enemy.