# Terminology

* **World:** The term used to describe a collection of robots and objects (such as buildings, tables, and lights), and global parameters including the sky, ambient light, and physics properties.
* **Static:** Entities marked as static (those having the `<static>true</static>` element in SDF), are objects which only have collision geometry. All objects which are not meant to move should be marked as static, which is a performance enhancement.
* **Dynamic:** Entities marked as dynamic (either missing the `<static>` element or setting false in SDF), are objects which have both inertia and a collision geometry.

Reference: <http://classic.gazebosim.org/tutorials?tut=build_world>


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