Power and distribution transformers are the heart of the power network. It is the core of the transmission and distribution system. Non-destructive investigation of its health status, especially for mechanical deformations, is a vital operation to guarantee continuous and efficient operation. The frequency response analysis (FRA) is gaining wider acceptance as an accurate approach of detecting different types of premature faults, deflections, and unbalances. This paper presents an informative but concise review of the fundamental terminology, essential test techniques, and the results analysis approaches. Such a review is valuable for researchers and engineers. Furthermore, the paper navigates the most promising and critical research topics in transformer status diagnosis using FRA.