GUI elements in JavaFX are ordered in a hierarchical tree-like fashion on a scene. The bottommost element is called the root element or root node, and in the majority of cases, this will be a container node (or pane), comprising child nodes that can be container nodes in turn, or leaf nodes that represent purely graphical elements like texts or images, and controller nodes like text input fields, buttons, sliders, or other.
The UI elements all get called nodes, but for clarity we sometimes name container nodes just ...