A liquid layer refers to a thin, continuous sheet or coating of liquid that forms on top of another substance. This term is commonly used in various fields such as chemistry, biology and physics where liquids are involved. In everyday life, you may have seen a liquid layer forming on the surface of water when oil is added to it - this is an example of a natural emulsion process that occurs between two immiscible liquids. Liquid layers can also form in industrial processes such as distillation or extraction where a liquid solvent is used to separate components from a mixture, with one component dissolving in the liquid layer while the other remains undissolved. In biology, a liquid layer may refer to the cell membrane which acts as a barrier between the cell's interior and exterior environments. Overall, the term "liquid layer" refers to any thin film or coating of liquid that forms on top of another substance or object.