circularity

Circularity is the quality or state of being circular. It can refer to geometric shapes, logical arguments, and systems designed to operate in cycles of reuse and regeneration.

In geometry, circularity describes how closely a two‑dimensional figure resembles a circle. A common quantitative measure is the circularity index, defined as 4πA/P^2, where A is area and P is the perimeter. Values near 1 indicate a shape that is very circle‑like.

In logic and rhetoric, circularity (often called circular reasoning) is a fallacy in which the conclusion rests on premises that assume the conclusion itself, providing little or no independent evidence.

In software, engineering, and planning, circularity can describe circular dependencies or feedback loops, where components depend on each other in a cycle. Such dependencies can complicate development, testing, and maintenance unless managed through design patterns or tooling.

In environmental and industrial contexts, circularity is a goal of the circular economy: to keep products, components, and materials in use, minimize waste, and reduce resource extraction. Strategies include repair, remanufacturing, refurbishing, remaking, and recycling, along with design for longevity and disassembly.

As a metric, circularity is used in material flow analysis and urban planning to assess how effectively systems recover and reuse resources. The concept emphasizes reducing entropy in material use and extending the lifespan of products within a closed loop.