Hi Deeno,
You are right neutrophils and poly are different names of the same type of WBCs.
"Neutrophils are a type of white blood cell also known as polymorphonuclear leukocytes". http://www.medicinenet.com/neutropenia/article.htm
As you can see in the article the Absolute Neutrophil Count (ANC) is determined by the product of the white blood cell count (WBC) and the fraction of neutrophils among the white blood cells. For example, if the WBC is 10.0 and 70% are neutrophils, the ANC would be 7.0. We almost always discuss ANC so you don't have to learn about other ways to count neutrophils.
Your father's neutrophils are fighting infection and getting killed while they are killing bacteria. His bone marrow can't make new neutrophils fast enough. Neupogen could stimulate the bone marrow so it could produce more neutrophils.
Kind regards
Birgitta-A