802.11ac ( also known as 5G Wi-Fi ) is actually a fifth-generation Wi-Fi technology that has been standardized by IEEE.
This is actually an evolution of the previous standard, 802.11n which used to provide more bandwidth and more simultaneous spatial streams. This allows data transfer rates to support 802.11ac devices, which are much faster than that of 802.11n devices.
Where earlier Wi-Fi standards operate at 2.4 GHz frequency, 802.11ac operates exclusively in a 5 GHz frequency band. This helps to avoid interfering more with common 2.4 GHz devices, such as cordless phones, baby monitors, and older wireless routers.
Computers and mobile devices that support 802.11ac get the benefit from 5 GHz bandwidth, but other older wireless devices still have to communicate with an 802.11ac router at a slower speed.
The initial draft of 802.11ac standard was approved in 2012, but 802.11ac hardware was not released until 2013.
Initial 802.11ac standard (wave 1) supported maximum data transfer rate of around 1300 Mbps, or 1.3 Gbps , which used 3 spatial streams. It was quite fast compared to 802.11n whose maximum speed was around 450 Mbps.
It also meant that 802.11ac is the first Wi-Fi standard in which it has the capability to be faster than Gigabit Ethernet. At the same time, the second 802.11ac standard (wave 2) is going to come after this, which will support double the amount of bandwidth of wave 1 devices as well as it will also offer data transfer rates which is going to be up to 3470 Mbps .