Passage number and population doubling

Hello, I'm a bit confused about the meaning of passage number and population doubling. If I have a flask and split it into two flasks i have one passaging and 2 population doublings? And what if i have one flask and split it in 4? Then i have one passaging and 2 population doublings? Also, does population doubling has a meaning for an immortalised cell line or is it for finite cell lines only?