A membrane is a thin, flexible layer that separates different environments or compartments. It can be found in various biological systems, such as the cell membrane, which surrounds and protects cells, allowing selective movement of substances in and out. Membranes can also be artificial, used in applications like filtration and separation processes. In addition to biological functions, membranes play a crucial role in technology. For example, polymer membranes are used in water purification systems, while lipid bilayers are studied in biophysics to understand cellular processes. Overall, membranes are essential for both life and various industrial applications.