Difference between pre-fit and post-fit

ROOT
1

Hi Friends,

Any one could please explain me a bit about post-fit and pre-fit.
Why it is needed? What happens after post-fit?

Cheers

pre-fitpost-fit

2

some one could please respond me.

3

It looks like you should ask the author of these plots (someone in ATLAS ?).

4

I need answer in general the difference between post-fit and pre-fit.