In the context of cell biology: any way to break up cells. Most common methods include blending, pressure or shear rupturing, and sonication (the use of sound to rupture the cells).
A common task prerequisite to many methods for further analysis of a cell culture. For example, centrifugation, in the form of equilibrium density centrifugation or velocity sedimentation centrifugation, to separate various parts of the cells based on their physical properties.