The term band is thrown around constantly in ham radio discussion and it is included in many questions in US license exam pools. So what exactly is a radio band?
Parts of the radio frequency spectrum allocated for a common purpose are called a band. Besides amateur radio, the reader may be familiar with USA commercial broadcast ranges known as AM band and the FM band, or another personal communication chunk of frequencies called the citizens band (CB).
With amateur radio, bands are generally associated with a number (2m or 40m, for example). This number is approximately equal to the wavelength of that span of frequencies
We say approximately because a specific wavelength is only valid at one exact frequency and that may be outside the actual range of the band.
Shown below is a chart of the current US amateur bands (dated 2017):
These 18 bands are are named by their approximate wavelength. For those who care about such details, the named wavelength (λ) may not actually be inside the designated frequency range. A table of these is given below:
Some do, but why don’t all the meter bands line up with wavelengths inside the band?
Lots of discussion on this issue can be found on the internet and two particularly good links are given in the first two references below. It’s a real combination of history, simplicity, misuse, and existing broadcast band names.
0.7m is the same as 700mm or 70cm; the 70cm name is more commonly used Continue reading
The red and blue sine waves are the 
For the center of one popular HF band the wavelength would be: 300/14.2=21m See how it works?
You can see how the yellow wavelength values above the blue frequencies increase in opposite directions. Note also how the values line up in 1/10/100s and 3/30/300s per the speed of light relationship.
NewHams.info 