Plain English Meaning
The different kinds of ground a pilot flies over -- flat land, hills, mountains, water, trees, and so on. Each one changes how the airplane handles and what to watch out for.
Full Definition
The general categories of land surface a pilot may operate over or near, each presenting distinct hazards and handling considerations. Common terrain types in aviation training include flat terrain, sloping terrain, hilly terrain, mountainous terrain, water (open and confined), and tree-covered or forested terrain. Each type affects takeoff and landing technique, performance planning, wind behavior, visual references, and emergency landing options.