Fluidization is a unit operation, and through this technique a bed of particulate solids, supported over a fluid-distributing plate (often called the grid), is made to behave like a liquid by the passage of the fluid (gas, liquid, or gas–liquid) at a flow rate above a certain critical value. In other words, it is the phenomenon of imparting the properties of a fluid to a bed of particulate solids by passing a fluid through the latter at a velocity which brings the fixed or stationary bed to its loosest possible state just before its transformation into a fluidlike bed.