In architecture and decorative art, ornament is decoration used to embellish parts of a building or object. Large figurative elements such as monumental sculpture and their equivalents in decorative art are excluded from the term; most ornaments do not include human figures, and if present they are small compared to the overall scale. Architectural ornament can be carved from stone, wood or precious metals, formed with plaster or clay, or painted or impressed onto a surface as applied ornament; in other applied arts the main material of the object, or a different one such as paint or vitreous enamel may be used.

A wide variety of decorative styles and motifs have been developed for architecture and the applied arts, including pottery, furniture, metalwork. In textiles, wallpaper and other objects where the decoration may be the main justification for its existence, the terms pattern or design are more likely to be used. The vast range of motifs used in ornament draw from geometrical shapes and patterns, plants, and human and animal figures. Across Eurasia and the Mediterranean world there has been a rich and linked tradition of plant-based ornament for over three thousand years; traditional ornament from other parts of the world typically relies more on geometrical and animal motifs. The inspiration for the patterns usually lies in the nature that surrounds the people in the region. Many nomadic tribes in Central Asia had many animalistic motifs before the penetration of Islam in the region.

In a 1941 essay, the architectural historian Sir John Summerson called it "surface modulation". The earliest decoration and ornament often survives from prehistoric cultures in simple markings on pottery, where decoration in other materials (including tattoos) has been lost. Where the potter's wheel was used, the technology made some kinds of decoration very easy; weaving is another technology which also lends itself very easily to decoration or pattern, and to some extent dictates its form. Ornament has been evident in civilizations since the beginning of recorded history, ranging from Ancient Egyptian architecture to the assertive lack of ornament of 20th century Modernist architecture. Ornaments also depict a certain philosophy of the people for the world around. For example, in Central Asia among nomadic Kazakhs, the circular lines of the ornaments signalled the sequential perception of time in the wide steppes and the breadth and freedom of space.

Ornament implies that the ornamented object has a function that an unornamented equivalent might also fulfill. Where the object has no such function, but exists only to be a work of art such as a sculpture or painting, the term is less likely to be used, except for peripheral elements. In recent centuries a distinction between the fine arts and applied or decorative arts has been applied (except for architecture), with ornament mainly seen as a feature of the latter class.