Prefab
A preconfigured template for a game object that you instantiate as many times as you like — edit the template and every copy follows.
The term was popularised by Unity (2005), where a prefab is a saved object complete with its components, values and children. Godot calls the equivalent a scene, Unreal uses blueprints and actors. The point is to separate authoring from instances: a tower is edited in one place and the thousand towers already on the map update with it.
Nested prefabs and prefab variants let a base be inherited and overridden locally — a red tower that inherits everything but the colour. Without them, changes become a copy-paste nightmare in which one forgotten copy always survives carrying stale values.