In materials science, the “active surface” refers to those areas of a material that exhibit increased reactivity. This can mean, for example, that the surface of a material has special chemical groups or functions that enable it to react with other substances. An active surface can also be created by special treatment of the material, such as heating, etching or coating.

In chemistry, the term "active surface" refers to the totality of all active sites on the surface of a catalyst. A catalyst is a substance that increases the speed of a chemical reaction. An increased active surface area in a catalyst means that there are more catalytically active sites, resulting in a higher reaction rate.

In both cases, the term "active surface" refers to the fact that the surface of a material or catalyst is not just passive, but actively involved in a specific chemical reaction.