Rigid or rigidity may refer to:

** Mathematics and physics **

*Stiffness, the property of a solid body to resist deformation, which is sometimes referred to as rigidity
*Structural rigidity, a mathematical theory of the stiffness of ensembles of rigid objects connected by hinges
*Rigidity (electromagnetism), the resistance of a charged particle to deflection by a magnetic field
*Rigidity (mathematics), a property of a collection of mathematical objects (for instance sets or functions)
*Rigid body, in physics, a simplification of the concept of an object to allow for modelling
*Rigid transformation, in mathematics, a rigid transformation preserves distances between every pair of points

** Medicine **

*Rigidity (neurology), an increase in muscle tone leading to a resistance to passive movement throughout the range of motion
*Rigidity (psychology), an obstacle to problem solving which arises from over-dependence on prior experiences

** Other uses **

*Real rigidity, and nominal rigidity, the resistance of prices and wages to marketchanges in macroeconomics
*Ridgid, a brand of tools
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