Singletons, Statics, GameObjects, and the World - Mastering Unity Scripting - page 92

So, GameObjects are composed of components. At a higher level, scenes are
composed of a collection of GameObjects inside a single world space. Furthermore,
objects themselves exist in an important relationship with each other, as defined
by the scene hierarchy. Objects can be the children of others, who are in turn their
parents ( transform.parent ). This relationship has important implications for how
objects move and transform. In short, values for an object's Transform component
will cascade downwards and be added to the transform of all its children. In this
way, a child GameObject is always offset and transformed relative to its parent;
the parent position is the origin of the child position. However, if an object has
no parent, then it would be transformed away from the world origin at (0, 0, 0).
The following screenshot shows the Hierarchy panel:
GameObjects exist in a scene hierarchy that determines their transformations