Optical equivalent path refers to the concept of optical path length, which is influenced by the refractive index of materials like glass and water, causing light to slow down and its wavelength to shorten. This change affects how physical distances are perceived in applications such as interference. The term "optical equivalent path" appears to be synonymous with "optical path length," as indicated by a limited search that yielded few results beyond this discussion. The phrase was found in a U.S. patent application related to camera technology. Understanding these terms is essential for grasping the behavior of light in different media.