Difference between DPLL and PLL

[Altera_Forum]

HI!:) 

I saw the topic in another webpage with ambiguous answers, I thought It's interesting. So I hope someone to make it more clear. Thanks!   What is PLL ? What are it's applications ?  What is the difference in analog & digital PLL ?  Why in VLSI circuits PLL is used?

[Altera_Forum]

DPLL (digital PLL) or ADPLL (all digital PLL) is usually referring to a time discrete system. The output signal is updated synchronous to a system clock, thus a timing jitter is introduced for frequencies that aren't an integer fraction of the system clock. 

 In my view, the main application of DPLLs is in the generation of low and medium frequency signals.