The Wifi Alliance expands the 802.11ac wifi standard with "Wave 2"-- essentially a means to boost current wifi bandwidths while retaining backwards compatibility.
According to the alliance Wave 2 doubles the bandwidth per channel to double performance should conditions be favourable. It also has four spatial streams, wider 5GHz channel support and MU-MIMO (multi-user, multiple input multiple output) support.
“In today’s world, people have more wifi devices per person and per household, and those devices require significantly more bandwidth,” the alliance says. “Wifi Alliance updated the wifi ac program to meet increasing user demands and to stay ahead of emerging applications, while preserving interoperability.”