CIR may refer to:
The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.
A circadian rhythm /sɜːrˈkeɪdiən/ is any biological process that displays an endogenous, entrainable oscillation of about 24 hours.
Cirrhosis is a condition in which the liver does not function properly due to long-term damage. This damage is characterized by the replacement of normal liver tissue by scar tissue.
Cirque du Soleil (pronounced: [sɪʁk dzy sɔ.lɛj], "Circus of the Sun" or "Sun Circus") is a Canadian entertainment company.
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current, typically resulting from an overload or short circuit.
A circle is a simple closed shape in Euclidean geometry. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant.