Frequency Synthesizer - dual modulus prescaler

[e-bedlam]

Please can anyonw explain what is Dual Modulus prescaler and how does it work. Cant find any proper link for it.
Thanks in advance

 

[FvM]

Edaboard is poor man's Google?

When I see statements like this, I use to check what Wikipedia knows about the topic. In my view, it's not bat as a basic explanation https://en.wikipedia.org/wiki/Dual-modulus_prescaler