A Wi-Fi adapter is a device that allows computers and other electronic devices to connect to a wireless network. It can be built into the device or added externally via USB or other ports. The adapter converts data from the device into a format that can be transmitted over radio waves, enabling internet access without physical cables. Wi-Fi adapters come in various types and speeds, supporting different Wi-Fi standards like 802.11n or 802.11ac. They are essential for devices that lack built-in wireless capabilities, such as older computers or desktop PCs, making it easier to access the internet from anywhere within the network's range.