What is reconnaisseance?

Answer 1

A preliminary survey, usually executed rapidly and at relatively low cost, prior to mapping in detail and with greater precision.

Answer 2

Reconnaissance is Scouting. Gathering information. Recon sections will normally go well forward of the main body to gather intelligence. Is there a road there? Is it dirt, gravel or paved? Bridges, rivers, or ditches? If there's a bridge will it hold a tank? If there's a river, can it be crossed by the unit?

Only the best officers and men will go on reconnaissance; they must answer ALL questions that the following army (unit) will encounter. If the recon party's Intel is faulty; the following unit (army) will suffer the consequences.

All branches use recon: Naval warships, mostly destroyers and cruisers; Air Force reconnaissance flights, and the Army and Marines.