DFRC (dual-function radar-communication) is proposed to overcome spectrum conflicts, hardware redundancy, and electromagnetic compatibility bottlenecks inherent in traditional separated architectures through hardware resource sharing and isomorphic signal waveform design, whereby the integrated operational effectiveness and battlefield survivability of platforms are significantly enhanced. The evolution of DFRC technology from its conceptual inception, through architectural advancements, to system implementation was systematically reviewed. The DFRC waveform design methodologies based on mainstream signal schemes were analyzed emphatically, including linear frequency modulation, orthogonal frequency division multiplexing, and orthogonal time frequency space. Furthermore, various sensing-centric waveform design criteria were explored in depth, such as beampattern matching, Cramér-Rao bound minimization, information-theoretical design, and so on. The engineering roadmap from software-defined radio compatibility verification and airborne multimodal waveform fusion to multi-node and multi-domain cooperation was summarized, clearly illustrating the theoretical-to-practical transition of DFRC. Through presenting the complete technical evolution of the DFRC system from the conventional single-input single-output system to multiple-input multiple-output system, and then to the prototype demonstrations, this overview provides systematic theoretical guidance and practical references for future research and development of DFRC systems.