+A fluid is a substance that continuously deforms under an applied [shear stress](/wiki/shear_stress), unable to resist tangential forces. It flows, adapting to the shape of its container, and includes both [liquids](/wiki/liquid) and gases. The study of fluids is central to fields from engineering to biology.
+## See also
+- [Gas](/wiki/gas)
+- [Liquid](/wiki/liquid)
+- [Viscosity](/wiki/viscosity)
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