As information technology advances and environmental protection becomes a priority, the concept of reliability needs to be redefined and expanded. Trustability, along with its applications, models, and prospects, is presented in simple terms. This note marks the beginning of broader and more active research in the field of reliability in the years to come. In this chapter, we have introduced a new mathematical concept called trustability. With the rapid advancement of technology and increasing demand for high-tech solutions, including AI, we believe the trustability function can be applied to many complex systems. These systems require not only reliability but also user trust, making trustability essential in various applications.