Histograms

I remember learning about histograms in school, I loved that I could understand them.  

I remember reading about them in the camera manual and being dismayed that I couldn't understand the concept.  Yesterday a friend mentioned them again.  So today I was a little haunted by the meaninglessness of that little graph on the screen.

Then I discovered something whilst playing around with ISO and aperture settings.  When I like the shape of the histogram, I also like the image!  What's that about?  Still no idea what it means though.

The abstract watery images I take are probably my favourites.  Anyone expecting a trademark sunset here it is.