Wi-Fi backscatter communication offers a compelling solution for ultra-low-power and battery-free communication systems, especially within the Internet of Things (IoT) domain. By repurposing existing Wi-Fi infrastructure and ambient signals, backscatter systems achieve energy-efficient communication by reflecting signals rather than generating them. This review consolidates the current landscape of Wi-Fi backscatter technologies and highlights key areas of development such as feasibility on commercial hardware, antenna design, modulation techniques, synchronization, and safe Wi-Fi packet manipulation. Furthermore, the review identifies persistent research gaps and proposes future directions to bridge them, with emphasis on addressing four core challenges: hardware feasibility, antenna optimization, modulation reliability, and protocol-safe Wi-Fi packet analysis.