so what exactly is const supposed to mean?

[Hasan Aljudy]

Ok, I know that the const issue has apparently been beaten to death on 
the digitalmars.D NG, but ....

Can someone please explain to me what does const mean? and doesn't D 
already have a const keyword?
I think it's something from C++, no? what is it? what does it do? and 
why do people think it's useful?

(hmm, I have a feeling that I've asked this before, but can't really 
remember)

While you're at it, would you mind explaining the implications of 
implemeting the proposed "const by default" feature?