The five Wi-Fi (802.11) technologies (a, b, g, n and ac) are often abbreviate as b/g/n, a/b/g/n and a/b/g/n/ac in the specifications for wireless routers, Wi-Fi access points and Wi-Fi in portable devices.
802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11 b, 802.11 a, 802.11 g, 802.11 n and 802.11 ac versions to provide wireless connectivity.
802.11 ax is designed to operate in all ISM bands between 1 and 7 GHz when they become available for 802.11 use, in addition to the 2.4 and 5 GHz bands already allocated. This is expected to be released in late 2019s.
Using the 5 GHz band gives a significant advantage, since the 2.4 GHz band is heavily used to the point of being crowded