Radio spectrum is divided up into channels. In the 2.4 GHz spectrum there are 14 channels, with channels 1, 6, 11 and 14 being non-overlapping. As described above in terms of bandwidth, the first channel in the 802.11g protocol begins at 2.400 GHz and ends at 2.422 GHz for a total bandwidth of 22 MHz. The first channel is then described as being centered at 2.412 GHz.
Channel availability is determined by region, with North America only having legal use of channels 1-11 while Europe and most of the world may use channels 1-13. Japan is special and gets access to all of the channels including 14 all to itself.
The 5 GHz spectrum is much more complicated in regards to bandwidth and channel availability by region with further restrictions on indoor/outdoor use. In the United States the FCC designates U-NII (Unlicensed National Information Infrastructure) bands 1-3 available, with 45 channels in total operating in 20, 40, 80 and 160 MHz bandwidth.
The WiFi Pineapple NANO operates in the 2.4 GHz band while the WiFi Pineapple TETRA operates in both the 2.4 and 5 GHz bands.
It’s also important to note that similar to modes of operation, a radio can only occupy one channel at a time. For this reason channel hopping is necessary in order to obtain a complete picture of the given spectrum. For example when performing a Recon scan, the WiFi Pineapple will switch one of its radios into monitor mode to passively listen on a channel. The radio will take a moment to note any data of interest on each channel before moving on to the next.