question about the significance of in/out ratio fro Google
 

Hi guys,
Thanks to the other tread I find some nice SEO tools and I am grateful for that. :)
I like rustybrick thing, but I still have to get familiar with some points. First is at "backlinks analysis" one parameter is in/out. Can someone explain what is that. For sure are not the number of links, because I have pages with no external links showing a ratio by 1 and pages with lot of links showing ratio of zero.
And also, can you enlight me with the significance of this ratio for listings ?
Thanks in anticipation
Sadman