Modo 14.0v2 docs:

Adding Layer Items

Modo scenes are basically collections of items: cameras, lights, meshes, locators, and so on. They are also referred to as layers. You can tell Modo what particular item you wish to edit by selecting them. When selected, their associated attributes appear in a Properties Panel panel where you can manipulate their values directly. For information on a specific item, click a link.

Icon	Name	Description
	Scene Item	The topmost layer of a Modo file.
	Fractal Gasket	A plug-in item type that generates various geometric arrays of objects.
	Gear Item	A plug-in item type that generates accurate procedural gear and cog shaped geometry.
	Ground Plane	An item that generates a flat plane.
	Group Locator Item	A locator that does not draw anything in the 3D viewport, eliminating scene clutter.
	Instance Item	A virtual duplicate of a Mesh Item.
	Locator Item	Items serving various functions in animation, such as targets, controllers, parents, and manipulators.
	Mesh Item	The model itself, consisting of vertices, edges, and polygons.
	Replicator Item	Replicators generate render time duplicates of geometry in a scene.
	RPC Mesh Item	A Rich Photoreal Content item that enhances the complexity and depth of a scene.
	Static Mesh Item	A non-editable object.