Surface energy, also known as interfacial energy, is a property of the surface or interface between two different phases of matter, such as a solid-liquid, liquid-gas, or solid-gas interface. It arises due to the cohesive forces between atoms or molecules within a material.

In a bulk material, the atoms or molecules are surrounded by neighboring particles in all directions, resulting in a balanced distribution of forces and no net force acting on each particle. However, at the surface or interface of the material, the particles experience unbalanced forces, as there are no neighboring particles on one side. As a result, the particles at the surface or interface have higher potential energy compared to those in the bulk.

Surface energy is the measure of this excess potential energy per unit area at the surface or interface. It is denoted by the symbol γ (gamma) and is measured in units of joules per square meter (J/m²) or dynes per centimeter (dyn/cm).