An 802.11 (Wi-Fi) router that uses the 2.4 GHz and 5 GHz frequency bands.  Prior to 802.11n, dual-band routers handled 802.11a users in the 5 GHz band, while simultaneously supporting 802.11b and 802.11g users in the 2.4 GHz band.
Dual-Band N Routers
A dual-band N router supports both bands for 11n, as well as previous 802.11 standards (a, b and g).  Such routers can provide load balancing; for example, data might be configured to transmit on the 2.4 GHz band (SSID #1), while video uses the 5 GHz band (SSID #2).  See 
wireless router, 
802.11n, 
802.11ac, 
802.11, 
Wi-Fi designations and 
SSID.
    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
Simultaneous Routing in Both Bands
Buffalo Technology's Nfinity Dual Band router simultaneously runs 11n and 11a at 5 GHz along with 11n and 11b/g at 2.4 GHz.  To balance the network load, network administrators determine which band to dedicate to 11n users.  (Image courtesy of Buffalo Technology Inc.)