Active layer is a term commonly used in scientific and technical fields, especially in the context of materials science and geology. It refers to the layer or region of a material or substrate that is most directly involved in the physical or chemical processes under study. Synonyms for active layer can vary depending on the specific application or discipline. For instance, in soil science, the active layer may be called the biologically active zone, while in electronics, it may be referred to as the conductive layer. Other possible synonyms for the active layer may include active surface zone, reaction zone, or functional layer.