The five Wi-Fi (802.11) technologies (a, b, g, n and ac) are often abbreviated BGN, ABGN and A/B/G/N/AC in the specifications for wireless routers, Wi-Fi access points and the Wi-Fi in portable devices.  For example, "N" means 802.11n.
Multiple Radio Chains (2x2, 4x2)
The 802.11n and 802.11ac technologies support multiple antennas, and a "2x2" or "4x2" in the specification means two transmitting and two receiving or four transmitting and two receiving antennas.  For more information, see 
Wi-Fi, 
802.11, 
wireless router and 
dual-band router.
   802.11      Frequency
   Standard    Band
   11a         5 GHz
   11b         2.4 GHz
   11g         2.4 GHz
   11n         2.4 GHz and 5 GHz
   11ac        5 GHz