Introductory USD terminology

While the vocabulary range of USD is massive, this section contains a few commonly used terms to help serve as a baseline. If you are new to USD, use the terms below as a basic starting point in grasping core workflow concepts as you begin working with USD in Maya. For further reading, please see Pixar's Introduction to USD and Pixar USD Glossary.

Common USD terms

• Stage – A loaded scenegraph, which can contain multiple Layers.
• Layer – The atomic persistent container of scene description for USD. Currently, layers must be saved to a file on disk.
• Anonymous Layer – An unsaved, newly created layer. Maya allows for layers to temporarily exist without a file on disk.
• Prim (Primitive) – The basic container for USD objects such as properties, data, other Prims, etc.
• Composition – The process of assembling multiple layers together by the composition arcs that relate them to each other, resulting in a Stage scenegraph of Prims.
• Composition Arcs – the "operators" that allow USD to create rich compositions of many layers contain mixes of "base" scene description and overrides. The six kinds of arcs are subLayers, inherits, variantSets, references, payloads, and specializes (a subset of inherits).
• Proxy (USD) – A prim paired with model that can be used as a level of detail (LOD) stand-in while still allowing inspection of the full model.
• Proxy (Maya) – A leaf node in the Outliner DAG to which the USD stage is attached under. Operations to the Proxy node trigger UFE calls to interact with Maya and USD.

Related Concepts: Maya's USD documentation covers workflows and windows that are unique to Maya, but it does not include a complete USD glossary or a complete overview of USD concepts. We've adopted USD-specific terminology to keep the experience consistent for advanced users, but these terms may be unfamiliar to beginners. If you're new to USD concepts, please see Pixar's Introduction to USD and Pixar USD Glossary for a great primer.