An ornamental structure is one which exists primarily or largely for the purpose of aesthetic enhancement of the landscape. This includes most fountains, some monuments, and a few other types of structures.

The ornamental usage is generally excluded when a structure is built for commemorative purposes, or when it is intended as a work of art. For example, an arch can be used for either ornament or commemoration. A sculpture is normally an artwork, but some sculptures (especially non-unique works) are used mainly for ornament.

For this usage, it is not sufficient for a structure to be designed with ornamental qualities; decoration of the landscape must be a principal purpose of its existence.