802.11ac (also known as 5G Wi-Fi) is a fifth-generation Wi-Fi technology that IEEE has standardized.
This evolution of the previous standard, 802.11n, provided more bandwidth and simultaneous spatial streams. This allows data transfer rates to support 802.11ac devices, which are much faster than 802.11n devices.
Earlier Wi-Fi standards operate at 2.4 GHz frequency, 802.11ac operates exclusively in a 5 GHz frequency band. This means it avoids interfering with more than common 2.4 GHz devices, such as cordless phones, baby monitors, and older wireless routers.
Computers and mobile devices that support 802.11ac 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 the 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 can 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 are going to be up to 3470 Mbps.