Étendues

Étendue is a French noun meaning extent, spread, area, or scope. It designates the size or reach of something, whether geographic (l'étendue d'un territoire), thematic (l'étendue d'un problème), or administrative (l'étendue de sa compétence). In literature and everyday language, étendue often evokes vastness, as in étendues sauvages or the open expanse. The plural étendues is used when referring to multiple extents or broad areas.

Etymology and usage: the word derives from the verb étendre, meaning to extend, via the past participle étendu; the noun étendue is the feminine form. It is used across fields to express breadth in both concrete and figurative senses, and appears in formal prose, legal language, geography, philosophy, and poetry.

In optics and physics, étendue denotes a specific technical concept: the optical étendue, defined as the product of a surface area A and the solid angle Ω over which light from that surface is emitted or accepted. Often written as AΩ, it is a fundamental invariant in lossless optical systems and constrains how much light can be transmitted or imaged. The concept links geometry to radiometry and informs lens design, illumination, and fiber-optic applications.

Examples include: l'étendue du territoire, l'étendue de son pouvoir, and les étendues de steppe. The term’s versatility means it can describe measurable size, theoretical reach, or practical capacity, from everyday speech to technical discourse.