The term "optional equipment" refers to additional features or accessories that can be added to a product, but which are not necessary for its basic function. These items may include things like specialized wheels, GPS systems, upgraded sound systems, and more. The phrase is often used in the context of purchasing cars, where buyers have the option to add on various features that can enhance their driving experience or make certain tasks easier. In essence, "optional equipment" refers to any feature that is not required for a product's basic functioning but which may be desirable for some consumers.