Pervasive sensing is a key enabling technology for the Internet of everything. However, conventional sensing modalities, constrained by cost, power consumption, and deployment complexity, struggle to serve as the sensing cornerstone for this vision. Battery-free radio frequency identification (RFID) sensing technology, leveraging its unique advantages such as battery-free operation, low cost, miniaturization, and inherent ID capability, demonstrates significant potential in transitioning from a mere "identity identifier" to a versatile "sensing terminal", thereby offering a new technological paradigm for pervasive sensing. This paper systematically reviews the evolution of this technology, covering its progression from fundamental applications like identity management to advanced frontiers including spatial perception, behavior recognition, environmental sensing, and health monitoring. Finally, the paper discusses the core challenges this technology faces in terms of performance, intelligent integration, and security & privacy, and outlines its future prospects as a key enabling technology for the internet of things.