Wireless Fidelity (Wi-Fi) is particularly popular today. Every place has hotspots to access the internet via Wi-Fi, including homes, offices, colleges, and other public places. This increased number of users, and hence the use of bandwidth, has led to radio spectrum congestion. Thus, in the year of 2011, Light-Fidelity (Li-Fi) was introduced, which applies a visible light region for data transmission, to solve this radio crisis problem. This visible part of the spectrum was 10,000 times big compared to the part utilized in the Wi-Fi radio. Furthermore, Li-Fi was a sub-set of Visible Light Communication (VLC), using Light-Emitting Diode (LED) bulbs for transmitting data utilizing light-medium. This paper reviews the differences between Li-Fi technology and wireless types. It Also focuses on the architecture, components, functioning, modulation technologies, and applications of Li-Fi. Index Terms—Li-Fi, VLC, Wi-Fi, LED, Photodetector, Optical wireless Communication