A strength of WiFi is it's ability to change what frequency it operates on based on traffic in different frequencies
The frequency ranges are called channels

There are 14 overlapping channels in the 2.4GHz range
There are 4 non-overlapping channels for 2.4GHz (1, 6, 11, 14)

The reason we don't use channels in the middle is primarily because the frequencies overlap
There is also something called channel width with 5GHz. Channel width controls the amount of frequencies used

There are 25 non-overlapping 20MHz channels in the 5GHz range
There are 12 non-overlapping 40MHz channels in the 5GHz range
There are 6 non-overlapping 80MHz channels in the 5GHz range
There are 2 non-overlapping 160 MHz channels in the 5GHz range