Dual channels (bounded channels): If channel width >= 40 MHz, the network uses dual-channels. That means it uses two channels in the reality. Due to the old standard, it is called as a single channel (for example channel 6), however it is located on somewhere else. In this example, the network uses channel 2 and 6 while the middle of the channels is on channel 4.
WiFi Analyzer app uses the next form to display it: X. ch (Y) where X is the old (single) channel and Y is the middle of the two channels. In that example: 06.ch (04)
I think a picture is more than 1000 words, so just look at this screenshot.
Disable secondary adjacent channel: Using this you can use the old style where a dual-channel network is display as it would be a single channel network.