Surface plasmons are coherent oscillations of free electrons that occur at the interface between a metal and a dielectric material, such as air or glass. These oscillations can be excited by light, leading to enhanced electromagnetic fields at the surface. This phenomenon is crucial in various applications, including plasmonic sensors and optical devices. When light hits a metal surface at a specific angle, it can couple with the surface plasmons, creating a wave that travels along the surface. This interaction is utilized in technologies like surface plasmon resonance (SPR), which is widely used for detecting biomolecular interactions in real-time.