This is the 5188th most frequent Polish word.
prócz
"Prócz" means "besides" or "except for" in English.
In this context, prócz also means 'other than the expected', indicating an unexpected addition.
Prócz zaproszonych gości przyszło kilka nieoczekiwanych osób.
Besides the invited guests, a few uninvited people showed up.
Prócz in this sentence is used to indicate exclusion, meaning 'except' or 'besides something specific'.
Nie mam nic prócz książki.
I have nothing except the book.
Here, prócz introduces an additional aspect, meaning 'aside from' or 'in addition to something'.