In chemistry, a suspension is a heterogeneous system consisting of a solid dispersed phase (made up of particles larger than 1 micrometer) distributed within a continuous liquid phase. In simple terms, it is a mixture in which tiny solid particles are dispersed in a liquid without dissolving.

Unlike solutions, where the solute is completely dissolved, in suspensions the particles remain physically separate and can be seen under an optical microscope. When left undisturbed, the particles tend to settle due to gravity, separating from the liquid phase. For this reason, suspensions are unstable over time and usually require shaking before use.

Common examples include mud, orange juice with pulp, or certain liquid pharmaceutical formulations containing insoluble active ingredients. Suspensions can be prepared in the laboratory or on an industrial scale using dispersion techniques and often require stabilizing agents (such as surfactants) to slow down sedimentation.

From a rheological perspective, suspensions may exhibit non-Newtonian behavior, especially when the solid concentration is high. They are widely used in chemistry, food processing, cosmetics, and pharmaceuticals, where it’s important to combine the properties of a solid with the handling ease of a liquid.