A substrate is a term used in various fields of knowledge, and its definition varies depending on the context). Here are some examples of what a substrate can mean:

• Chemistry: In chemistry, a substrate can refer to a chemical species being observed in a chemical reaction, or to a surface on which other chemical reactions or microscopy are performed. In the former sense, a reagent is added to the substrate to generate a product through a chemical reaction. In biochemistry, an enzyme substrate is the material upon which an enzyme acts).
• Material sciences: In material sciences, the word “substrate” is often used to describe the base of the material on which various processing are carried out under specified reaction parameters to form new layers and films such as coatings.
• Biology: In biology, a substrate can be the surface on which an organism lives or the substance on which an enzyme can act. The substrate is also known as the foundation to which an immobile substance is attached in ecology.

In summary, a substrate is a term used to describe the underlying substance or layer upon which a chemical reaction, biological process, or other phenomenon occurs.