It is an emphatic demonstrative pronoun meaning that. However it is on the lofty side, perhaps a bit archaic and rarely encountered in colloquial specch.
Eg: Pamiętam ów dzień, kiedy...( I rememebr that day, when...)
I misunderstood you so I have to edit my post. The word "ów" is old-fashioned and reraly used in the present. You can use "ów" when you don't want to repeat yourself ans say all the time ...ze...ze...ze and when you want to sound more eloquent.
No! 'Ów' can be used in meaning 'that one', and it doesn't mean 'że'!!! E.g.:
That man was looking at me: Tamten człowiek patrzył na mnie. or Ów człowiek patrzył na mnie (that man (the one I was mentioning earlier) was looking at me)
BUT:
He said that he comes tomorrow. Powiedział, że przyjdzie jutro. BUT NEVER: !!!!!! Powiedział, ów przyjdzie jutro. !!!!!!! IT'S WRONG!!!!!!