In real-time computer graphics, geometry instancing is the practice of rendering multiple copies of the same mesh in a scene at once.
This technique is primarily used for objects such as trees, grass, or buildings which can be represented as repeated geometry without appearing unduly repetitive, but may also be used for characters.
This method improves the potential runtime performance of rendering instanced geometry by explicitly allowing multiple copies of a mesh to be rendered sequentially by specifying the differentiating parameters for each in a separate stream.
Geometry instancing in offline rendering is useful for creating things like swarms of insects, in which each one can be detailed, but still behaves in a realistic way that does not have to be determined by the animator.
In Houdini, many object level attributes (e.g. such as scale) can also be varied on a per instance basis.