pore

A pore is a small opening that allows the passage of gas or liquid through a surface or boundary. Pores occur in living organisms, minerals and rocks, and synthetic materials, and they can range from microscopic to visible in size.

In biology, skin pores are openings in the epidermis connected to hair follicles and sebaceous glands, through which sweat and oil can reach the surface. In plants, pores refer to stomata, usually on the undersides of leaves, which regulate gas exchange and water loss by opening and closing in response to environmental conditions.

In geology and soil science, pores are the void spaces within rocks and soils that can store and transmit fluids. Porosity is the fraction of a rock or soil volume that is pore space, while permeability describes how readily fluids can move through connected pores. Pore pressure and pore water influence geotechnical behavior, groundwater flow, and hydrocarbon reservoirs.

In materials science, pores are intentionally engineered in foams, membranes, catalysts, and filters to control surface area, diffusion pathways, and transport properties. Pore size distributions distinguish micropores (<2 nanometers), mesopores (2–50 nanometers), and macropores (>50 nanometers). Pore morphology and connectivity affect processes such as filtration, catalysis, and drying.

The term pore is used in various disciplines to describe openings or voids that enable transport or storage of liquids and gases. Proper characterization of pore size, shape, and connectivity is essential for understanding phenomena in health, geology, and engineering.