Can someone explain "Cholecalciferol" in an easy to understand lingo

I'm just curious and I looked it up online and don't really get it! what does it mean when it says D3 in cholecalciferol form? Thanks 

Basically, D3 in Cholecaciferol form is the purest form of D we can take--it is like what we create from the sun.  D2 is less effective in treating deficiencies.  

Here's a pretty decent and clear explanation:  http://www.vitamindcouncil.org/about-vitamin-d/what-is-vitamin-d/

Great thanks...I get it now!!