What is "theoretical plate"

n. (context physics chemistry English) A plate or tray in a distillation column that produces the best possible difference between the liquid and vapour phases in equilibrium with it; the equivalent concept in a fractionating column packed with beads or rings

A theoretical plate in many separation processes is a hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an equilibrium with each other. Such equilibrium stages may also be referred to as an equilibrium stage, ideal stage, or a theoretical tray. The performance of many separation processes depends on having a series of equilibrium stages and is enhanced by providing more such stages. In other words, having more theoretical plates increases the efficiency of the separation process be it either a distillation, absorption, chromatographic, adsorption or similar process.