:I believe the person is talking about the fact that under the heading of Definition, the word "null" appears multiple times.  Also, instead of explaining the meaning or the word, that section seems to express a whole formula for using a null set. Perhaps the mathmaticians' interpretation of the word "definition" is a little different than what we're expecting the word to mean?  As for myself, when I saw in the introduction that the word "null" meant "negligable," I assumed at first that it was something like a remainder of .2 when splitting a whole item amoung four people: unimportant.  Then I looked at the Definition section, and saw, appearently, instructions use.    
 :Anyways, can we get a definition written for those of us who just want to know generally what people who say "null set" are talking about?  For instance, I wanted to know what greater and less than signs were called when used like parentheses.  I found the term in question, but my husband told me that a null set was something in math.  So I looked it up, to learn what it is. Instead, I'm leaving this page with the impression that a negligable amount is not something left over, but something you want to work with ... and I don't know why you want to work with it ... it's unimportant ... right?   
 :I guess we're asking, "Dilbert ..., where's Tina?"  
 :(PS, They're called angle brackets!).