The term "postbiotics" has been increasingly used in scientific literature and commercial products, yet a standardized definition remains elusive. In 2021, the International Scientific Association for Probiotics and Prebiotics issued a consensus statement on the definition of postbiotics, which has achieved broad international recognition and application, but some scholarly debate remained. This article re-evaluated the postbiotic concept through scientific, commercial, and regulatory lenses, proposing the definition as "a preparation of inanimate microorganisms and/or their components that confers a scientifically substantiated human health benefit. " Meanwhile, the conceptual framework underpinning this definition was systematically elaborated. Furthermore, we consolidated criteria for postbiotics selection and evaluation method ologies. We critically synthesized clinical trial evidence demonstrating efficacy across multiple health domains, including: gastrointestinal disorders, constipation, immune modulation and upper respiratory infections, metabolic diseases, oral and skin health, etc. Then, mechanistic insights were analyzed through three key pathways: modulation of gut microbiota composition/function, enhancement of intestinal barrier integrity, regulation of immune system responses. Collectively, this work provided an evidence-based foundation to advance postbiotic research, industrial development, and standardization efforts.