802.11 is a set of technical specifications for networking and wireless communication, standardized by IEEE.
There are many versions and optional parts of 802.11, but the most common and well-known by far are those that define Wi-Fi, the global standard for wireless local-area networks (WLAN). The core standards for Wi-Fi include 802.11n (Wi-Fi 4), 802.11ac (Wi-Fi 5), and 802.11ax (Wi-Fi 6).
There are other, optional parts of 802.11 that enhance service on enterprise/campus Wi-Fi networks, among other functions. For example, higher-end phones may support 802.11r, which enables faster handoffs for devices in motion, and/or 802.11k which enables devices to more intelligently select the access point that will provide the best service.