Definition: A core set of technologies combined into a single software package to accelerate game development. A full game engine typically includes a graphics renderer, a network layer, a sound engine, a physics system, a scripting language/interpreter, and a graphical previewer/editor. Some more advanced engines will incorporate shader editors, terrain systems, and other, more advanced, features.
Examples:
Epic's UDK and Unity's Unity Engine are both examples of modern, cross-platform engines.
