Reconnaissance is the act of gathering information before committing to a higher-risk action. In game design, it usually means sending units, moving cautiously, probing for responses, or otherwise spending time and resources to reduce uncertainty. It becomes especially valuable in games with asymmetric-information, fog-of-war, or hidden threats, where knowledge itself behaves like a resource (Björk & Holopainen, Patterns in Game Design, see source-patterns-in-game-design).
Related: asymmetric-information, fog-of-war, stealth, risk-reward, meaningful-decisions